[Bug #19426] Fix endless `Range#step` with `#succ` method

	Ensure IO.copy_stream buffer is an independent string

	Otherwise, changes to the buffer by the destination write method
	could result in data changing for supposedly independent strings.

	Fixes [Bug #21131]

[Bug #21170]

st_table reserves -1 as a special hash value to indicate that an entry
has been deleted. So that that's a valid value to be returned from the
hash function, do_hash replaces -1 with 0 so that it is not mistaken for
the sentinel.

Previously, when upgrading an AR table to an ST table,
rb_st_add_direct_with_hash was used which did not perform the same
conversion, this could lead to a hash in a broken state where one if its
entries which was supposed to exist being marked as a tombstone.

The hash could then become further corrupted when the ST table required
resizing as the falsely tombstoned entry would be skipped but it would
be counted in num entries, leading to an uninitialized entry at index
15.

In most cases this will be really rare, unless using a very poorly
implemented custom hash function.

This also adds two debug assertions, one that st_add_direct_with_hash
does not receive the reserved hash value, and a second in
rebuild_table_with, which ensures that after we rebuild/compact a table
it contains the expected number of elements.

Co-authored-by: Alan Wu <alanwu@ruby-lang.org>

	Avoid opt_aset_with optimization inside multiple assignment

	Previously, since the opt_aset_with optimization was introduced,
	use of the opt_aset_with optimization inside multiple assignment
	would result in a segfault or incorrect instructions.

	Fixes [Bug #21012]

	Co-authored-by: Nobuyoshi Nakada <nobu.nakada@gmail.com>

	[Bug #21008] Normalize before sum to float

	After switching to `Float`-mode when summing `Numeric` objects,
	normalization for `Float` is still needed.

	[Bug #20995] Protect `IO.popen` block from exiting by exception

	[Bug #20984] ENV.inspect should be encoding aware

	[Bug #20984] Fix test with locale encoding

	[Bug #20924] Fix reading with delimiter in wide character encodings

	[Bug #20915] Fix SEGV with `TracePoint#parameters` and aliased C method

	The following snippet results with a SEGV:

	```ruby
	C = Class.new do
	  alias_method :new_to_s, :to_s
	end

	TracePoint.new(:c_call, &:parameters).enable { C.new.new_to_s }
	```

	at MRI 3.3.6 and ruby 3.4.0dev

	The root cause of the issue lies in the `rb_tracearg_parameters` function
	within the `RUBY_EVENT_C_RETURN` branch. Specifically, when the invoked
	method is an alias for a C function,
	`rb_method_entry_without_refinements(..., trace_arg->called_id, ...)`
	may return NULL. In that case we can fallback to `trace_arg->id`.