feat(version-scanner): support target list inputs via --targets

[chalmerlowe]

This pull request adds support for scanning multiple target dependencies and versions concurrently via a YAML file containing targets, while consolidating file handling and error logging.

Key changes:

• YAML Targets File Support: Adds a --targets-file CLI argument to read and resolve multiple target dependency-version tuples from a configuration file.
• Consolidated File Handling: Centralizes file reading and error logging across the codebase under a single helper (_safe_read_file) with uniform stderr printing and exit codes.
• Expanded Test Coverage: Adds parametrized unit tests validating targets file parsing errors (missing files, bad format, null values) and the core file helper error branches, and updates integration tests to utilize soft-fail flags.

[gemini-code-assist]

Code Review

This pull request introduces support for scanning multiple dependency targets simultaneously via a new --targets CLI argument, which accepts either a YAML/JSON file path or an inline string. It updates the scanning, rule resolution, and CSV reporting logic to handle multiple targets, and adds comprehensive unit tests. The review feedback highlights two critical issues where calling os.path.exists() on inline JSON/YAML strings containing invalid path characters can cause the script to crash on Windows. Additionally, the reviewer recommends improving error handling for non-existent target files and validating parsed version types to prevent unexpected scanning behavior.