Update composer lifecycle

[alganet]

• Commit composer.lock.
• The lock is not ignored anymore.
• Changed to ramsey/composer-install action for cache.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.56%. Comparing base (b701fac) to head (db4d8b5).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #1678   +/-   ##
=========================================
  Coverage     99.55%   99.56%           
- Complexity      966      970    +4     
=========================================
  Files           192      193    +1     
  Lines          2269     2280   +11     
=========================================
+ Hits           2259     2270   +11     
  Misses           10       10           

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[Copilot]

Pull request overview

This PR updates the project’s Composer dependency lifecycle by committing the resolved dependency lockfile, ensuring it is no longer ignored by Git, and switching CI dependency installation to a dedicated Composer install action with caching.

Changes:

• Add and commit composer.lock to lock dependency resolution.
• Stop ignoring composer.lock in .gitignore and mark it under REUSE annotations.
• Update the CI setup composite action to use ramsey/composer-install@v3 instead of manually running composer install.

Reviewed changes

Copilot reviewed 2 out of 4 changed files in this pull request and generated no comments.

File	Description
composer.lock	Adds a locked dependency graph for reproducible installs.
REUSE.toml	Includes composer.lock in REUSE annotations.
.gitignore	Ensures composer.lock is tracked in Git.
.github/actions/setup-action/action.yml	Switches Composer install to ramsey/composer-install@v3 (enables caching).

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