feat(engine): make String.prototype.repeat respect loop iteration limit

[alienx5499]

This Pull Request fixes/closes #5060.

It changes the following:

• Charge built-in iteration loops against the existing loop budget so they respect Context::set_loop_iteration_limit
• Use IncrementLoopIteration::operation((), context) inside String.prototype.repeat so large repeat counts consume the VM loop budget and throw RuntimeLimitError::LoopIteration when the limit is exceeded
• Add tests that:
  • Verify normal behavior is unchanged when no loop limit is set
  • With a small loop limit, both a plain JS loop and String.prototype.repeat throw the same RuntimeLimitError::LoopIteration
  • Include a regression test for a large repeat count to ensure the limit prevents unbounded work without panicking or hanging

Testing:

• cargo test -p boa_engine (including the new runtime-limit tests for built-in iteration)

[github-actions]

Test262 conformance changes

Test result	main count	PR count	difference
Total	52,963	52,963	0
Passed	49,935	49,935	0
Ignored	2,207	2,207	0
Failed	821	821	0
Panics	0	0	0
Conformance	94.28%	94.28%	0.00%

Tested main commit: 50373f1c00129f6d2bb654241185f8e20e10a333
Tested PR commit: b7c53675db34e431fe74284ba1c7a70f0f219785
Compare commits: 50373f1...b7c5367

[alienx5499]

Hi @jedel1043,

CI checks have passed for this PR. When you have some time, I’d appreciate a review.

This change focuses on the minimal entry point mentioned in the issue String.prototype.repeat to ensure builtins implemented with Rust loops correctly charge the VM loop iteration budget. If this approach looks good, I can follow up with additional PRs auditing other builtins that iterate internally.

[jedel1043]

You forgot to carry over the with_capacity

[alienx5499]

I’ve restored Vec::with_capacity(n) in the latest commit.

[jedel1043]

Looks good!

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 59.09%. Comparing base (6ddc2b4) to head (b7c5367).
⚠️ Report is 852 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #5069       +/-   ##
===========================================
+ Coverage   47.24%   59.09%   +11.85%     
===========================================
  Files         476      563       +87     
  Lines       46892    62574    +15682     
===========================================
+ Hits        22154    36981    +14827     
- Misses      24738    25593      +855     

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