Add Cron.prev reverse iteration support

[kitlangton]

Summary

• add backward cron traversal with shared lookup tables and last-boundary resets
• align DST handling while walking backward and add reverse sequence iterator
• expand cron prev/next symmetry tests, DST overlap coverage, step/range backward cases, month/year wrap, and add changeset

Context

Based on @tmcw's fork branch https://github.com/tmcw/effect/tree/cron-prev ; rebased on main and tightened tests/edge cases.
Closes #5666.

Testing

• pnpm vitest packages/effect/test/Cron.test.ts

[changeset-bot]

🦋 Changeset detected

Latest commit: 5b7e465

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 36 packages

Name	Type
effect	Minor
@effect/cli	Major
@effect/cluster	Major
@effect/experimental	Major
@effect/opentelemetry	Major
@effect/platform-browser	Major
@effect/platform-bun	Major
@effect/platform-node-shared	Major
@effect/platform-node	Major
@effect/platform	Major
@effect/printer-ansi	Major
@effect/printer	Major
@effect/rpc	Major
@effect/sql-clickhouse	Major
@effect/sql-d1	Major
@effect/sql-drizzle	Major
@effect/sql-kysely	Major
@effect/sql-libsql	Major
@effect/sql-mssql	Major
@effect/sql-mysql2	Major
@effect/sql-pg	Major
@effect/sql-sqlite-bun	Major
@effect/sql-sqlite-do	Major
@effect/sql-sqlite-node	Major
@effect/sql-sqlite-react-native	Major
@effect/sql-sqlite-wasm	Major
@effect/sql	Major
@effect/typeclass	Major
@effect/vitest	Major
@effect/workflow	Major
@effect/ai	Major
@effect/ai-amazon-bedrock	Major
@effect/ai-anthropic	Major
@effect/ai-google	Major
@effect/ai-openai	Major
@effect/ai-openrouter	Major

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[kitlangton]

@copilot tell me I'm beautiful

[Copilot]

@kitlangton I've opened a new pull request, #5787, to work on those changes. Once the pull request is ready, I'll request review from you.