Add test.cleanup() and test.cleanupEach() for reliable cleanup tasks

[stevenmini2019]

Summary

Implements reliable cleanup tasks for #928. Adds two new chain methods:

• test.cleanup(fn) — registers fn as both a before hook and an after.always hook. The after.always half always runs, even when a test fails or --fail-fast aborts the run, so idempotent cleanup code can rely on it to remove state left behind by the current (or a previously crashed) run.
• test.cleanupEach(fn) — registers fn as both a beforeEach hook and an afterEach.always hook, so it runs around every test.

Both are also available on test.serial (test.serial.cleanup, test.serial.cleanupEach) and support .skip().

Why this design

The root problem in #928 is that after/.always hooks are not guaranteed to run after a failure or when a process exits/crashes mid-run, leaving stale fixtures behind. By pairing a before (or beforeEach) registration with an after.always (or afterEach.always) registration, the cleanup code is guaranteed to run on the way out — this is the contract test.cleanup() and test.cleanupEach() provide.

Implementation

• lib/create-chain.js — adds a createCleanupChain helper that wires cleanup/cleanupEach into both root and root.serial, with .skip() support.
• lib/runner.js — the chain-metadata callback now recognizes the cleanup/cleanupEach task types and pushes the implementation into two task arrays: before + afterAlways (for cleanup) and beforeEach + afterEachAlways (for cleanupEach). The after halves are flagged always: true so they run even on failure.
• types/test-fn.d.ts — adds a CleanupFn type and exposes cleanup/cleanupEach on TestFn and SerialFn.
• test-types/module/conditional-chains.ts — type-level coverage for the new chains.
• test/create-chain/test.js — metadata-level assertions (runs in CI).
• test/cleanup/test.js — runtime integration test proving the dual execution, including the on-failure guarantee.
• docs/01-writing-tests.md — documents test.cleanup() / test.cleanupEach().

Verification

• xo passes on all modified files.
• test/cleanup/test.js passes locally: cleanup runs as before + after.always, cleanupEach runs around every test, and a failing test still triggers the after.always half (the core guarantee of this feature).

Notes / open question

Unlike the previously-open PR #3457 (which only touched create-chain.js and never connected the runtime), this wires the behavior all the way through runner.js so the hooks actually execute. Happy to adjust the API surface (e.g. method names) if maintainers prefer a different convention.

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IssueHunt Summary

Referenced issues

This pull request has been submitted to:

• #928: Make it easier to write reliable cleanup tasks

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