ci: upgrade actions/cache from v3 to v4

[paul58914080]

Checklist for self review:

• My code follows the contribution guidelines of this project
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• My commits follow conventional commit message guidelines

[Copilot]

Pull Request Overview

Upgrade GitHub Actions cache from v3 to v4 in the build workflow to keep CI dependencies current.

• Bump actions/cache to v4 for Maven dependency caching

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[Copilot]

Pin the action to a specific commit SHA instead of the mutable v4 tag to prevent supply-chain risk and unexpected behavior when the tag is updated. Example: uses: actions/cache@ with an inline comment noting the version.

[Copilot]

Add restore-keys to improve cache reuse when pom.xml changes, reducing cold builds. For example: restore-keys: | (newline) ${{ runner.os }}-maven-

[Copilot]

actions/setup-java supports built-in Maven caching (cache: maven). Enabling it on the setup-java step can simplify the workflow and eliminate the separate actions/cache step.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.22%. Comparing base (83dfcd7) to head (0e4db79).
⚠️ Report is 78 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #565      +/-   ##
============================================
+ Coverage     87.69%   89.22%   +1.53%     
- Complexity      188      204      +16     
============================================
  Files            51       51              
  Lines           520      594      +74     
  Branches         21       21              
============================================
+ Hits            456      530      +74     
  Misses           53       53              
  Partials         11       11              

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