[ryanchou1994]

Fixes #301

Proposed Changes

DoubleMetaphone drops the S in is, giving both is and a the code ['A', 'A']. The silent-S condition currently skips S whenever it follows A/I or precedes L. Restrict that exception to the complete ISL and YSL sequences so ordinary S sounds are retained.

Add regressions for is, as, asleep, and leslie, with controls for silent S, initial SL, French final S, comparison, and code truncation. Other letter rules and the public API are unchanged.

Validation on macOS and Linux: the new tests produce 6 failures against the original code, then all 107 DoubleMetaphone specs and 867 unit specs pass with the fix. TypeScript and ESM builds, lint, Standard JS, jscpd, and CJS/ESM smoke checks pass. Database-backed IO tests were not run; this change only affects phonetic encoding.

Checklist before merging

• Added Jasmine tests
• Updates TypeScipt index.d.ts files — not needed; no type or API changes.

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