#492: Use Maven dependency cache in CI workflows

[krystynaShatkovska]

This PR fixes TodoIssueID

Implemented changes:

Added cache: 'maven' to the setup-java@v5 step in build.yml, build-pr.yml, mutation-test.yml, and the deploy job of nightly-build.yml, so these jobs restore a shared ~/.m2/repository dependency cache instead of re-downloading all Maven dependencies on every run. This matches the convention already used in release.yml, update-cve.yml, and update-urls.yml.
The cache is keyed on the hash of the pom.xml files (handled automatically by setup-java), so it is reused while dependencies are unchanged and only re-created when they change

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Testing instructions

1. Open this PR, expand the CI Build PR run -> Set up JDK step. Look for the cache line. It should be a hit ("Cache restored successfully…") because main's CI has already cached this dependency set (the pom.xml files are unchanged from main). A miss only occurs the first time a new dependency set is ever cached.
2. On Checks , then hover CI Build PR, then Re-run jobs. The re-run (same commit, same pom.xml) should log a hit again, with a minimal Maven download.
3. Confirm the Set up JDK step / total run is noticeably faster than a cold run, most artifacts restored, not re-downloaded.

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Checklist for this PR

Make sure everything is checked before merging this PR. For further info please also see
our DoD.

• When running mvn clean test locally all tests pass and build is successful
• PR title is of the form #«issue-id»: «brief summary» (e.g. #921: fixed setup.bat and not feature/921 fixed setup.bat). If no issue ID exists, title only.
• PR top-level comment summaries what has been done and contains link to addressed issue(s)
• PR and issue(s) have suitable labels
• Issue is set to In Progress and assigned to you or there is no issue (might happen for very small PRs)
• You followed all coding conventions
• You have added the issue implemented by your PR in CHANGELOG.adoc unless issue is labelled
  with internal
• You have not changed any dependency in pom.xml files or otherwise if runtime dependencies changed, you have updated our LICENSE.asciidoc
• You have formulated clear instructions on how to test your contribution under "Testing instructions"

[coveralls]

Coverage Report for CI Build 33744754508

Coverage increased (+0.03%) to 73.826%

Details

• Coverage increased (+0.03%) from the base build.
• Patch coverage: No coverable lines changed in this PR.
• No coverage regressions found.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

No coverage regressions found.

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Coverage Stats

Relevant Lines:	18583
Covered Lines:	14336
Line Coverage:	77.15%
Relevant Branches:	8276
Covered Branches:	5493
Branch Coverage:	66.37%
Branches in Coverage %:	Yes
Coverage Strength:	3.29 hits per line

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💛 - Coveralls