Add tests for non-primitive set operator HashMap paths to fix coverage regression

[Copilot]

Codecov project check fails because the ES2025 Set fast-path optimizations in $setEquals/$setIsSubset left the HashMap fallback (non-primitive elements) untested, dropping project coverage from 99.59% → 99.50%.

• $setEquals: Added object-array tests covering the HashMap path for both equal (true via line 44) and size-mismatch (false via line 42) cases
• $setIsSubset: Added object-array subset test triggering the early-termination branch (line 36)

All existing tests used primitive values, so the native Set.isSubsetOf() fast path was always taken. These four new cases force the HashMap codepath:

// $setEquals — HashMap path returns true
[[[{ a: 1 }, { b: 2 }], [{ b: 2 }, { a: 1 }]], true],
// $setEquals — HashMap path, size mismatch
[[[{ a: 1 }, { b: 2 }], [{ a: 1 }]], false],
// $setIsSubset — HashMap early termination
[[[{ a: 1 }], [{ a: 1 }, { a: 2 }]], true],

Coverage after: setEquals.ts 85% → 100%, setIsSubset.ts branch 90% → 100%.

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