Previously, if GC was in progress when we're initially building the
id2ref table, it could see the empty table and then crash when trying to
remove ids from it. This commit fixes the bug by only publishing the
table after GC is done.

Co-authored-by: Aaron Patterson <tenderlove@ruby-lang.org>

Fix a regression introduced by: https://github.com/ruby/ruby/pull/13155

There's a lot of warnings when running test_objectspace.rb because of
ObjectSpace._id2ref. For example:

    test_objectspace.rb:19: warning: ObjectSpace._id2ref is deprecated

This inverse table is only useful if `ObjectSpace._id2ref` is used,
which is extremely rare. The only notable exception is the `drb` gem
and even then it has an option not to rely on `_id2ref`.

So if we assume this table will never be looked up, we can just
not maintain it, and if it turns out `_id2ref` is called, we
can lock the VM and re-build it.

```
compare-ruby: ruby 3.5.0dev (2025-04-10T09:44:40Z master 684cfa42d7) +YJIT +PRISM [arm64-darwin24]
built-ruby: ruby 3.5.0dev (2025-04-10T10:13:43Z lazy-id-to-obj d3aa9626cc) +YJIT +PRISM [arm64-darwin24]
warming up..

|           |compare-ruby|built-ruby|
|:----------|-----------:|---------:|
|baseline   |     26.364M|   25.974M|
|           |       1.01x|         -|
|object_id  |     10.293M|   14.202M|
|           |           -|     1.38x|
```

The test is timing out on lpi4a so a longer timeout should fix it.

We need to remove from the finalizer_table after running all the
finalizers because GC could trigger during the finalizer which could
reclaim the finalizer table array.

The following code crashes:

    1_000_000.times do
      o = Object.new
      ObjectSpace.define_finalizer(o, proc { })
    end

We don't need to treat static symbols in any special way since they
can't be confused with other special consts or GC managed objects.

This commit adds RVALUE_OVERHEAD for storing metadata at the end of the
slot. This commit moves the ractor_belonging_id in debug builds from the
flags to RVALUE_OVERHEAD which frees the 16 bits in the headers for
object shapes.