Add per-client Makefiles for C, Python, and Go with:
- CLI mode: Tests --help, arg parsing, syntax validation
- Library mode: Unit tests, import verification
- Integration mode: API contract validation (with credentials)
- Functional mode: Real-world scenario tests
C client:
- 22 library tests (SHA-256, HMAC-SHA256, detect_language)
- Full unsandbox.c implementation with examples
Python client (sync + async):
- Delegates to sync/ and async/ subdirectories
- pytest-based test suites with coverage
- Examples for concurrent execution, streaming
Go client:
- Delegates to sync/ and async/ subdirectories
- go test integration with vet and fmt
Also update detect-changes.sh to detect changes in
both root-level un.* files AND clients/ directory.
