Add matches/occursOn convenience helpers and Strict RFC enforcement option

[ggaabe]

Summary

• add matches() and occursOn() convenience helpers
• document new helpers in README
• add tests for exact instant, day-only, timezone, and rDate/exDate behavior
• Adds strict option for strict RFC adherence, defaults to false

Testing

• npm test -- src/tests/rrule-temporal.test.ts

---

Note

Introduces a toggleable strict RFC 5545 validation and convenience occurrence checks.

• Adds strict to rule options; enforces RFC 5545 constraints in enforceStrictRfc() (e.g., BYWEEKNO only with FREQ=YEARLY, BYYEARDAY restrictions, BYMONTHDAY not with WEEKLY, numeric BYDAY limits, and requiring BYSETPOS to pair with another BY*). Called from sanitizeOpts(); strict is propagated when parsing ICS.
• Adds matches(date) (exact-instant occurrence) and occursOn(PlainDate) (day-level check in rule tz). Both leverage between() and respect rDate/exDate.
• README: documents new strict option and the new API methods; test suite expanded to cover strict errors, helpers’ behavior, and timezone handling.

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