Claude review: kunit: Add documentation for warning backtrace suppression API

[Claude Code Review Bot <claude-review@example.com>]

Patch Review

**Good documentation.** All three API forms are documented with clear examples and the correct ordering (scoped first as recommended, direct last as most verbose).

**Nit:** The documentation adds a trailing newline to the final line of `usage.rst`:
```diff
-	}
\ No newline at end of file
+	}
```
This is a drive-by fix for a pre-existing missing newline. Fine, but it might cause a trivial merge conflict if another patch touches the end of this file.

**Overall assessment:** This is a well-designed, well-tested series at v8 maturity. The core infrastructure is sound, the API is clean, and the test coverage is thorough. The series is ready to merge with no blocking issues. The observations above are minor and mostly informational.

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Generated by Claude Code Patch Reviewer