[PATCH] [Bug #21629] Initialize `struct RString`

which appears to be missed in the previous commit for some reason.

	[PATCH] load.c: Fix dest and src of MEMMOVE

	When multiple files with the same name are required, the features_index
	hash stores the indexes in `$LOADED_FEATURES` array into a darray.
	The dest and src arguments for `MEMMOVE` were wrongly reversed when
	inserting a new index in the darray.

	[Bug #21568]

	Fix crash when $LOADED_FEATURES is modified during require

	[Bug #21567]

	When we require an object that is not a string, it will attempt to convert
	it to a string by calling to_str on it. If we modify the $LOADED_FEATURES
	array while it calls to_str, Ruby can crash because it can end up inserting
	the string in the wrong index in the array.

	For example, the following script crashes:

	    require "tempfile"

	    class MyString
	      def initialize(path)
	        @path = path
	      end

	      def to_str
	        $LOADED_FEATURES.clear
	        @path
	      end

	      def to_path = @path
	    end

	    def create_ruby_file = Tempfile.create(["test", ".rb"]).path

	    require MyString.new(create_ruby_file)
	    $LOADED_FEATURES.unshift(create_ruby_file)
	    $LOADED_FEATURES << MyString.new(create_ruby_file)
	    require create_ruby_file

	Crash log:

	    test.rb:21: [BUG] Segmentation fault at 0x0000000000000004
	    ruby 3.5.0dev (2025-09-09T09:29:35Z master ce94add7fb) +PRISM [arm64-darwin24]

	    -- Crash Report log information --------------------------------------------
	      See Crash Report log file in one of the following locations:
	        * ~/Library/Logs/DiagnosticReports
	        * /Library/Logs/DiagnosticReports
	      for more details.
	    Don't forget to include the above Crash Report log file in bug reports.

	    -- Control frame information -----------------------------------------------
	    c:0003 p:---- s:0011 e:000010 CFUNC  :require
	    c:0002 p:0076 s:0006 e:000005 EVAL   test.rb:21 [FINISH]
	    c:0001 p:0000 s:0003 E:0001b0 DUMMY  [FINISH]

	    -- Ruby level backtrace information ----------------------------------------
	    test.rb:21:in '<main>'
	    test.rb:21:in 'require'

	    -- Threading information ---------------------------------------------------
	    Total ractor count: 1
	    Ruby thread count for this ractor: 1

	    -- Machine register context ------------------------------------------------
	      x0: 0x0000000000000004  x1: 0x000000000000c800  x2: 0x0000000000000000
	      x3: 0x0000000000000000  x4: 0x0000000000000205  x5: 0x0000000000000000
	      x6: 0x0000000000000000  x7: 0x0000000000000001 x18: 0x0000000000000000
	    x19: 0x0000000209dfc0b0 x20: 0x0000000209dfc018 x21: 0x000000016ee8ab58
	    x22: 0x0fffffff0009d71d x23: 0x0000000209dfc018 x24: 0x0000000209dfc150
	    x25: 0x000000016ee8acc0 x26: 0x0000000000000000 x27: 0x0000000000000000
	    x28: 0x0000000000000000  lr: 0x0000000101244140  fp: 0x000000016ee887f0
	      sp: 0x000000016ee887d0

	    -- C level backtrace information -------------------------------------------
	    miniruby(rb_print_backtrace+0x24) [0x101317b08] vm_dump.c:843
	    miniruby(rb_print_backtrace) (null):0
	    miniruby(rb_vm_bugreport+0x26c) [0x101317d94] vm_dump.c:1175
	    miniruby(rb_bug_for_fatal_signal+0xa4) [0x10105ddac] error.c:1130
	    miniruby(sig_do_nothing+0x0) [0x1012278c0] signal.c:948
	    miniruby(sigsegv) (null):0
	    /usr/lib/system/libsystem_platform.dylib(_sigtramp+0x38) [0x19c1216a4]
	    miniruby(rb_str_new_frozen+0x1c) [0x101244140] string.c:1495
	    miniruby(rb_check_realpath_internal+0x68) [0x101077804] file.c:4679
	    miniruby(rb_check_realpath+0x2c) [0x101077aa4] file.c:4765
	    miniruby(get_loaded_features_index+0x37c) [0x1010f9c94] load.c:467
	    miniruby(rb_feature_p+0xd0) [0x1010f8174] load.c:582
	    miniruby(search_required+0xac) [0x1010f6ad4] load.c:1193
	    miniruby(require_internal+0x274) [0x1010f7518] load.c:1424
	    miniruby(rb_require_string_internal+0x94) [0x1010f6830] load.c:1571
	    miniruby(rb_require_string+0x58) [0x1010f66e8] load.c:1557
	    miniruby(rb_f_require+0x1c) [0x1010f6684] load.c:1150
	    miniruby(ractor_safe_call_cfunc_1+0x38) [0x101306c28] vm_insnhelper.c:3696
	    miniruby(vm_call_cfunc_with_frame_+0x250) [0x1012f857c] vm_insnhelper.c:3873
	    miniruby(vm_call_cfunc_with_frame+0x6c) [0x1012f8834] vm_insnhelper.c:3919
	    miniruby(vm_sendish+0x1a8) [0x1012c990c] vm_insnhelper.c:6087
	    miniruby(vm_exec_core+0x4050) [0x1012cfb48] insns.def:900
	    miniruby(vm_exec_loop+0x80) [0x1012e5448] vm.c:2666
	    miniruby(rb_vm_exec+0x134) [0x1012c9b40] vm.c:2645
	    miniruby(rb_iseq_eval_main+0x34) [0x1012e5628] vm.c:2919
	    miniruby(rb_ec_exec_node+0xe4) [0x10106d094] eval.c:282
	    miniruby(ruby_run_node+0x94) [0x10106cf64] eval.c:320
	    miniruby(rb_main+0x40) [0x100f7499c] main.c:42
	    miniruby(main+0x60) [0x100f74928] main.c:62

	rb_feature_p: skip `get_expanded_load_path` for absolute paths

	Ref: https://github.com/fxn/zeitwerk/pull/308

	```ruby
	require 'benchmark'

	$LOAD_PATH << 'relative-path'

	autoload :FOO, '/tmp/foo.rb'

	puts Benchmark.realtime {
	  500_000.times do
	    Object.autoload?(:FOO)
	  end
	}
	```

	The above script takes 2.5 seconds on `master`, and only
	50ms on this branch.

	When we're looking for a feature with an absolute path, we don't
	need to call the expensive `get_expanded_load_path`.

When searching for native extensions, if the name does not end in ".so"
then we create a new string and append ".so" so it. If the native extension
is in static_ext_inits, then we could trigger a GC in the rb_filesystem_str_new_cstr.
This could cuase the GC to free lookup_name since we don't use the local
variable anymore.

This bug was caught in this ASAN build:
http://ci.rvm.jp/results/trunk_asan@ruby-sp1/5479182

    ==435614==ERROR: AddressSanitizer: use-after-poison on address 0x715a63022da0 at pc 0x5e7463873e4e bp 0x7fff383c8b00 sp 0x7fff383c82c0
    READ of size 14 at 0x715a63022da0 thread T0
        #0 0x5e7463873e4d in __asan_memcpy (/tmp/ruby/build/trunk_asan/ruby+0x214e4d) (BuildId: 607411c0626a2f66b4c20c02179b346aace20898)
        #1 0x5e7463b50a82 in memcpy /usr/include/x86_64-linux-gnu/bits/string_fortified.h:29:10
        #2 0x5e7463b50a82 in ruby_nonempty_memcpy /tmp/ruby/src/trunk_asan/include/ruby/internal/memory.h:671:16
        #3 0x5e7463b50a82 in str_enc_new /tmp/ruby/src/trunk_asan/string.c:1035:9
        #4 0x5e74639b97dd in search_required /tmp/ruby/src/trunk_asan/load.c:1126:21
        #5 0x5e74639b97dd in require_internal /tmp/ruby/src/trunk_asan/load.c:1274:17
        #6 0x5e74639b83c1 in rb_require_string_internal /tmp/ruby/src/trunk_asan/load.c:1401:22
        #7 0x5e74639b83c1 in rb_require_string /tmp/ruby/src/trunk_asan/load.c:1387:12

If there's a syntax error during iseq compilation then prism would leak
memory because it would not free the pm_parse_result_t.

This commit changes pm_iseq_new_with_opt to have a rb_protect to catch
when an error is raised, and return NULL and set error_state to a value
that can be raised by calling rb_jump_tag after memory has been freed.

For example:

    10.times do
      10_000.times do
        eval("/[/=~s")
      rescue SyntaxError
      end

      puts `ps -o rss= -p #{$$}`
    end

Before:

    39280
    68736
    99232
    128864
    158896
    188208
    217344
    246304
    275376
    304592

After:

    12192
    13200
    14256
    14848
    16000
    16000
    16000
    16064
    17232
    17952

Many libraries should be loaded on the main ractor because of
setting constants with unshareable objects and so on.

This patch allows to call `requore` on non-main Ractors by
asking the main ractor to call `require` on it. The calling ractor
waits for the result of `require` from the main ractor.

If the `require` call failed with some reasons, an exception
objects will be deliverred from the main ractor to the calling ractor
if it is copy-able.

Same on `require_relative` and `require` by `autoload`.

Now `Ractor.new{pp obj}` works well (the first call of `pp` requires
`pp` library implicitly).

[Feature #20627]