test: add core WeakSet builtin unit tests

[mrhapile]

This PR introduces initial unit tests for the WeakSet builtin.

Currently the WeakSet implementation relies entirely on test262 coverage
and does not have internal Rust-level tests in the Boa engine.

This PR adds:

core/engine/src/builtins/weak_set/tests.rs

The following behaviors are tested:

• WeakSet.prototype.add basic functionality
• WeakSet.prototype.has
• WeakSet.prototype.delete
• add() chaining behavior

These tests follow the same structure used by other builtin tests
such as WeakMap, Map, and Set.

Additional edge case tests will be added in a follow-up PR.

[Copilot]

Pull request overview

Adds initial Rust-level unit tests for the WeakSet builtin in Boa’s core engine, complementing existing test262 coverage and aligning with the structure used for other builtin tests.

Changes:

• Introduces core/engine/src/builtins/weak_set/tests.rs with basic behavioral tests for add, has, delete, and add() chaining.
• Wires the new test module into the WeakSet builtin via #[cfg(test)] mod tests;.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
core/engine/src/builtins/weak_set/tests.rs	Adds initial unit tests covering core WeakSet prototype behaviors.
core/engine/src/builtins/weak_set/mod.rs	Registers the new tests submodule under cfg(test).

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[github-actions]

Test262 conformance changes

Test result	main count	PR count	difference
Total	52,963	52,963	0
Passed	49,902	49,902	0
Ignored	2,222	2,222	0
Failed	839	839	0
Panics	0	0	0
Conformance	94.22%	94.22%	0.00%

Tested main commit: 11b1cfa7e2bd5c3e2aec2293712dd734ec64bb95
Tested PR commit: a7f9a8205c9973b62a2db2473c456f481f5227c8
Compare commits: 11b1cfa...a7f9a82

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 57.73%. Comparing base (6ddc2b4) to head (31c0751).
⚠️ Report is 772 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #4912       +/-   ##
===========================================
+ Coverage   47.24%   57.73%   +10.49%     
===========================================
  Files         476      556       +80     
  Lines       46892    60739    +13847     
===========================================
+ Hits        22154    35068    +12914     
- Misses      24738    25671      +933     

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[jedel1043]

Superseeded by #4914