feat: support multi-value discriminant matching

[okyrychenko-dev]

Summary

• allow useEffectWhenMatch to accept a single discriminant value or a readonly array
• narrow matched dependencies to the union of selected variants
• treat an empty value array as never matching
• preserve existing once and onSkip behavior

Tests

• add multi-variant narrowing coverage
• verify transitions between matched values with once: false
• verify single-value and array-value onSkip behavior
• cover empty arrays, Strict Mode, and includes semantics for NaN

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!