refactor: Inline test data and group related test cases

- Move CMake test data from external files to inline here-strings
- Group related test scenarios into single test cases for better readability
- Reduce test count from 16 to 6 while maintaining same coverage
- Remove external testdata/cmake/ directory (no longer needed)
- Improve test maintainability - all test input/output visible in one place

Test groupings:
- Parse scenarios: basic, auto-detect, hash, complex formatting
- Multiple deps: auto-detection errors, explicit selection
- Error scenarios: missing deps, missing repo/tag
- Hash resolution: null results, network failures
- Update scenarios: tag-to-tag, hash-to-hash, complex formatting
- Update errors: missing dependency updates

Author: vaind