Add VersionMap utility methods and improve implementation

[billf]

Enhanced VersionMap with Additional Utility Methods

This PR enhances the VersionMap implementation with several new utility methods and improves the internal structure:

• Added standard collection methods:

  • len(), is_empty(), contains_version()
  • clear() to remove all versions
  • get_mut() for mutable access to values

• Added iteration capabilities:

  • versions() to iterate over all versions in sorted order
  • iter() to iterate over version-value pairs
  • get_first() to retrieve the lowest version and its value

• Improved internal implementation:

  • Implemented Default for VersionMap
  • Refactored insertion logic with helper methods
  • Optimized get() method to check for exact match first
  • Enhanced remove() to properly clean up alternates mapping

• Added comprehensive tests for all new functionality

These changes make VersionMap more complete and consistent with standard Rust collection types.

[billf]

• Add VersionMap utility methods and improve implementation #5 👈 (View in Graphite)
• master

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[Copilot]

Pull Request Overview

This PR enhances the VersionMap with new utility methods for size, emptiness, membership, mutation, and clearing; adds iteration helpers; refactors insertion and alternate tracking; optimizes lookup; and updates tests accordingly.

• Added standard collection methods (len, is_empty, contains_version, clear, get_mut, get_first) and iteration APIs (versions, iter).
• Refactored insertion logic into insert_internal/update_alternates, implemented Default, and optimized get to try exact match first.
• Improved remove to clean up alternate mappings and expanded test coverage for new behaviors.

Comments suppressed due to low confidence (2)

src/semver.rs:177

• [nitpick] After removing a version from the alternates set, consider removing its key when the set becomes empty to avoid leaving stale entries in alternates.

set.remove(version);

src/semver.rs:163

• [nitpick] Add a unit test for get_mut to verify that you can obtain and modify a stored value through a mutable reference.

pub fn get_mut(&mut self, version: &Version) -> Option<&mut T> {

[github-actions]

Code Coverage Report

Package	Base Coverage	New Coverage	Difference
graph.rs	🟢 81.85%	🟢 81.85%	⚪ 0%
path.rs	🟢 100%	🟢 100%	⚪ 0%
semver.rs	🟢 97.7%	🟠 69.51%	🔴 -28.19%
trampoline.rs	🟠 72.86%	🟠 72.86%	⚪ 0%
Overall Coverage	🟢 85.77%	🟢 80.41%	🔴 -5.36%

Minimum allowed coverage is 0%, this run produced 80.41%