This was missed when adding core Set, because it's handled
implicitly for T_OBJECT.

Keep marshal compatibility between core Set and stdlib Set,
so you can unmarshal core Set with stdlib Set and vice versa.

Co-authored-by: Nobuyoshi Nakada <nobu@ruby-lang.org>

If the provided Hash doesn't have a default proc, we know for
sure that we'll never call into user provided code, hence the
string we allocate to access the Hash can't possibly escape.

So we don't actually have to allocate it, we can use a fake_str,
AKA a stack allocated string.

```
compare-ruby: ruby 3.5.0dev (2025-02-10T13:47:44Z master 3fb455adab) +PRISM [arm64-darwin23]
built-ruby: ruby 3.5.0dev (2025-02-10T17:09:52Z opt-gsub-alloc ea5c28958f) +PRISM [arm64-darwin23]
warming up....

|                 |compare-ruby|built-ruby|
|:----------------|-----------:|---------:|
|escape           |      3.374k|    3.722k|
|                 |           -|     1.10x|
|escape_bin       |      5.469k|    6.587k|
|                 |           -|     1.20x|
|escape_utf8      |      3.465k|    3.734k|
|                 |           -|     1.08x|
|escape_utf8_bin  |      5.752k|    7.283k|
|                 |           -|     1.27x|
```

If a Hash which is empty or only using literals is frozen, we detect
this as a peephole optimization and change the instructions to be
`opt_hash_freeze`.

[Feature #20684]

Co-authored-by: Jean Boussier <byroot@ruby-lang.org>

Hashes are no longer allocated on the transient heap.

With VWA, AR hashes are much larger than ST hashes. Hash#replace
attempts to directly copy the contents of AR hashes into ST hashes so
there will be memory corruption caused by writing past the end of memory.

This commit changes it so that if a ST hash is being replaced with an AR
hash it will insert each element into the ST hash.

This allows Hashes with ST tables to fit int he 80 byte size pool.