feat: rrule and ruleset validate

[shavonn]

Add validate function for checking RRULE and RRuleSet strings without throwing.

• New validate(s, options?) function that returns { valid: true } or { valid: false, error: { message, cause } }
• Accepts the same string formats and options as rrulestr
• Exported ValidationResult, ValidationSuccess, and ValidationError types

[Copilot]

Pull request overview

This PR adds a new validate function to provide a safe, non-throwing way to validate RRULE and RRuleSet strings. The function wraps the existing rrulestr parser and returns a discriminated union indicating success or failure with detailed error information.

Changes:

• New validate function that accepts the same inputs as rrulestr but returns a validation result instead of throwing
• Three new TypeScript types exported: ValidationResult, ValidationSuccess, and ValidationError
• Comprehensive test coverage for both valid and invalid inputs, including edge cases

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/validate.ts	Implements the core validation function that wraps rrulestr in try-catch and returns structured validation results
src/index.ts	Exports the new validate function and associated TypeScript types
test/validate.test.ts	Comprehensive test suite covering valid inputs, invalid inputs, and contract guarantees (never throws)
README.md	Documentation for the validate function including usage examples and TypeScript type definitions
.changeset/heavy-times-turn.md	Changeset entry describing the new minor feature

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[Copilot]

Inconsistent package name in import statement. This line uses 'rrule' while the new validate examples added in lines 166 and 770 use '@offload-project/rrule'. Consider using the full package name '@offload-project/rrule' consistently throughout the documentation, or using the short form 'rrule' consistently.

Suggested change

	import { datetime, RRule, RRuleSet, rrulestr, validate } from 'rrule'
	import { datetime, RRule, RRuleSet, rrulestr, validate } from '@offload-project/rrule'