This PR refactors how tool versions/tags are stored and handled within dotbins to improve accuracy and enable future reproducibility features like lock file support.

Motivation:

Storing only the stripped version (e.g., 1.2.3) prevents reliable fetching of the exact release needed for reproducible installs, as the original tag (e.g., v1.2.3) is lost. Storing the exact tag name from GitHub ensures we can always reference the precise release state. This change lays the groundwork for potential "install from lock file" functionality.

Additionally, supporting both the full tag ({tag}) and the stripped version ({version}) in asset patterns provides greater flexibility for matching real-world asset naming conventions.

Key Changes:

1. VersionStore renamed to Manifest: The class responsible for storing installation state is now more accurately named Manifest.
2. Stores Exact Tag: The manifest.json (previously versions.json) now stores the exact Git tag name (e.g., v1.2.3) under the key "tag". A manifest format version ("version": 2) is also added.
3. New tag_to_version Utility: A helper function utils.tag_to_version() is introduced to derive the stripped version (e.g., 1.2.3) from a tag when needed.
4. Flexible Asset Patterns: asset_patterns in dotbins.yaml now support both:
   • {tag}: Expands to the full tag name (e.g., v1.2.3).
   • {version}: Expands to the stripped version name (e.g., 1.2.3).
5. Updated Comparison Logic: The logic to skip downloads (BinSpec.skip_download) now compares the stored full tag against the latest target full tag.
6. User Display: User-facing commands (status, readme, update summary) now use tag_to_version() to display the more conventional stripped version number (e.g., 1.2.3), even though the full tag is stored internally.
7. Tests Updated: All relevant tests have been updated to reflect the class renaming, stored field changes, and new logic.

Impact:

• The format of the versions.json file has changed. (Note: Since there are no users, this isn't a breaking change in practice, but it's a format evolution).
• Users configuring tools can now choose between {tag} and {version} in asset_patterns for optimal matching.

This change provides a more robust foundation for managing tool states accurately and paving the way for future enhancements.