These two class are most common sources of infinite sequences.  This change should effectively prevent accidental infinite loops when calling to_set on them. [Bug #21513]

ref: https://bugs.ruby-lang.org/issues/21644

```shell
$ ruby -v -e '("a" || "b").."c"'
ruby 3.4.7 (2025-10-08 revision 7a5688e2a2) +PRISM [x86_64-linux]
-e:1: warning: possibly useless use of .. in void context
-e:1: [BUG] Stack consistency error (sp: 7, bp: 6)
ruby 3.4.7 (2025-10-08 revision 7a5688e2a2) +PRISM [x86_64-linux]

-- Control frame information -----------------------------------------------
c:0002 p:0013 s:0007 e:000005 EVAL   -e:1 [FINISH]
c:0001 p:0000 s:0003 E:001920 DUMMY  [FINISH]

-- Ruby level backtrace information ----------------------------------------
-e:1:in '<main>'

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

-- C level backtrace information -------------------------------------------
ruby/3.4.7/lib/libruby.so.3.4(rb_print_backtrace+0x8) [0x78aa9573c882] /tmp/ruby-build.20251010151551.31019.jR04SY/ruby-3.4.7/vm_dump.c:823
ruby/3.4.7/lib/libruby.so.3.4(rb_vm_bugreport) /tmp/ruby-build.20251010151551.31019.jR04SY/ruby-3.4.7/vm_dump.c:1155
ruby/3.4.7/lib/libruby.so.3.4(rb_bug_without_die_internal+0x6b) [0x78aa9544c62f] /tmp/ruby-build.20251010151551.31019.jR04SY/ruby-3.4.7/error.c:1097
ruby/3.4.7/lib/libruby.so.3.4(rb_bug) /tmp/ruby-build.20251010151551.31019.jR04SY/ruby-3.4.7/error.c:1115
ruby/3.4.7/lib/libruby.so.3.4(vm_stack_consistency_error+0x1f) [0x78aa9544f091] /tmp/ruby-build.20251010151551.31019.jR04SY/ruby-3.4.7/vm_insnhelper.c:6523
ruby/3.4.7/lib/libruby.so.3.4(vm_get_cref) /tmp/ruby-build.20251010151551.31019.jR04SY/ruby-3.4.7/insns.def:1134
ruby/3.4.7/lib/libruby.so.3.4(vm_setclassvariable) /tmp/ruby-build.20251010151551.31019.jR04SY/ruby-3.4.7/vm_insnhelper.c:1630
ruby/3.4.7/lib/libruby.so.3.4(vm_setclassvariable) /tmp/ruby-build.20251010151551.31019.jR04SY/ruby-3.4.7/vm_insnhelper.c:1627
ruby/3.4.7/lib/libruby.so.3.4(vm_exec_core) /tmp/ruby-build.20251010151551.31019.jR04SY/ruby-3.4.7/insns.def:253
ruby/3.4.7/lib/libruby.so.3.4(vm_exec_loop+0xa) [0x78aa95724959] /tmp/ruby-build.20251010151551.31019.jR04SY/ruby-3.4.7/vm.c:2622
ruby/3.4.7/lib/libruby.so.3.4(rb_vm_exec) /tmp/ruby-build.20251010151551.31019.jR04SY/ruby-3.4.7/vm.c:2598
ruby/3.4.7/lib/libruby.so.3.4(rb_ec_exec_node+0xa5) [0x78aa95525695] /tmp/ruby-build.20251010151551.31019.jR04SY/ruby-3.4.7/eval.c:281
ruby/3.4.7/lib/libruby.so.3.4(ruby_run_node+0x83) [0x78aa95529333] /tmp/ruby-build.20251010151551.31019.jR04SY/ruby-3.4.7/eval.c:319
ruby/3.4.7/bin/ruby(rb_main+0x21) [0x59d86f5e0186] ./main.c:43
ruby/3.4.7/bin/ruby(main) ./main.c:68
/lib/x86_64-linux-gnu/libc.so.6(__libc_start_call_main+0x7a) [0x78aa9502a1ca] ../sysdeps/nptl/libc_start_call_main.h:58
/lib/x86_64-linux-gnu/libc.so.6(call_init+0x0) [0x78aa9502a28b] ../csu/libc-start.c:360
/lib/x86_64-linux-gnu/libc.so.6(__libc_start_main_impl) ../csu/libc-start.c:347
/lib/x86_64-linux-gnu/libc.so.6(__libc_start_main) (null):0
[0x59d86f5e01d5]
```

The optimization in question:

https://github.com/ruby/ruby/blob/957c832db137e67289e93dfd9fd9e915b1f2fc87/compile.c\#L3453-L3480

Before entering the `newrange` optimization, the iseq looks like this:

```
== disasm: #<ISeq:<compiled>@<compiled>:1 (1,0)-(1,17)>
0000 putchilledstring                       "a"                       (   1)[Li]
0002 dup
0003 branchif                               8
0005 pop
0006 putchilledstring                       "b"
0008 putchilledstring                       "c"
0010 newrange                               0
0012 leave
```

So the optimization constructs a new range using the wrong operands (`"b"` and `"c"` instead of `"a"` and `"c"`).

I tried to fix this by checking whether the two previous instructions are labeled.

Infinite ranges, i.e. unbounded ranges, should overlap with any other range
which wasn't the case in the following example: (0..3).overlap?(nil..nil)

When the end points of an inclusive range equal, `Range#step` should
yields the element once.

It means unbounded, always inclusive of other ranges.

Make Range#step to consistently use + for iteration [Feature #18368]

Previously, non-numerics expected step to be integer,
and iterated with begin#succ, skipping over step value
steps. Since this commit, numeric and non-numeric iteration
behaves the same way, by using + operator.