feat: add wrap helper

[MFA-G]

Closes #2.\n\n## Summary\n- add OnceStore.wrap(prefix, fn, options) with preserved argument/return types\n- derive default keys from the prefix plus stable JSON of the arguments, with custom key override support\n- document the wrapper API and add coverage for dedupe, custom keys, and retryable failures\n\n## Validation\n- npm test\n- npm run typecheck

[samuelagents]

Reviewed the wrap helper implementation and added a maintainer follow-up to harden default key derivation. The wrapper now avoids silent key collisions for non-plain arguments, uses toJSON values such as Date, and rejects unsupported default-key inputs with a clear custom-key error.\n\nValidation passed locally and in CI:\n- npm test\n- npm run typecheck\n- npm run build\n- CI green on Node 18, 20, and 22