feat(test): implement onTestFinished hook for bun:test (#24038)

## Summary

Implements `onTestFinished()` for `bun:test`, which runs after all
`afterEach` hooks have completed.

## Implementation

- Added `onTestFinished` export to the test module in `jest.zig`
- Modified `genericHook` in `bun_test.zig` to handle `onTestFinished` as
a special case that:
  - Can only be called inside a test (not in describe blocks or preload)
  - Appends hooks at the very end of the execution sequence
- Added comprehensive tests covering basic ordering, multiple callbacks,
async callbacks, and interaction with other hooks

## Execution Order

When called inside a test:
1. Test body executes
2. `afterAll` hooks (if added inside the test)
3. `afterEach` hooks
4. `onTestFinished` hooks ✨

## Test Plan

- ✅ All new tests pass with `bun bd test`
- ✅ Tests correctly fail with `USE_SYSTEM_BUN=1` (feature not in
released version)
- ✅ Verifies correct ordering with `afterEach`, `afterAll`, and multiple
`onTestFinished` calls
- ✅ Tests async `onTestFinished` callbacks

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

---------

Co-authored-by: Claude Bot <claude-bot@bun.sh>
Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
Co-authored-by: pfg <pfg@pfg.pw>

docs/cli/test.md

@@ -257,12 +257,13 @@ $ bun test --watch
 
 Bun supports the following lifecycle hooks:
 
-| Hook         | Description                 |
-| ------------ | --------------------------- |
-| `beforeAll`  | Runs once before all tests. |
-| `beforeEach` | Runs before each test.      |
-| `afterEach`  | Runs after each test.       |
-| `afterAll`   | Runs once after all tests.  |
+| Hook             | Description                                              |
+| ---------------- | -------------------------------------------------------- |
+| `beforeAll`      | Runs once before all tests.                              |
+| `beforeEach`     | Runs before each test.                                   |
+| `afterEach`      | Runs after each test.                                    |
+| `afterAll`       | Runs once after all tests.                               |
+| `onTestFinished` | Runs after a test finishes, including after `afterEach`. |
 
 These hooks can be defined inside test files, or in a separate file that is preloaded with the `--preload` flag.