Ensure hard reference for frozen strings

[headius]

These frozen strings must be hard referenced until the identity has been tested, or an intervening GC could cause them to get collected and improperly fail the test. The cross-require global now points at the string in question and is cleared after the identity test.

[headius]

Spurious failure in JRuby tests here was most likely due to unlucky GC timing. This should prevent such failures in the future:

https://github.com/jruby/jruby/actions/runs/22466746658/job/65074368459

[headius]

Now RuboCop doesn't like the object_id comparison, but that was the original expectation. Changing to equal? would be an equivalent test.

[herwinw]

Now RuboCop doesn't like the object_id comparison, but that was the original expectation. Changing to equal? would be an equivalent test.

For what it's worth: I think Rubocop has some value to keep the formatting/indentation consistent, but a lot of code in this repository is not idiomatic Ruby on purpose.
For Natalie, we've switched to syntax_tree, which is just formatting and nothing else. I'm honestly thinking this might be a better fit for ruby-spec too.

[eregon]

Looks good.
Let's switch to equal?, I think in general it's not good to compare object_ids anyway, and also requesting the object_id might have a side effect like adding the object in some weakmap on CRuby or so.

[headius]

Looks good. Let's switch to equal?, I think in general it's not good to compare object_ids anyway, and also requesting the object_id might have a side effect like adding the object in some weakmap on CRuby or so.

Will do and then merge.

[headius]

GHA is down again so I'm merging without the final run. Tested locally on 3.4 and 4.0, it should be fine.