Improve publication workflow

[Lipen]

This PR adds GitHub Actions workflow for publishing snapshot of neo branch to GitHub Packages repository.

• Artifact group is default, org.jacodb.
• Artifact IDs correspond to sub-project names (default behavior of maven-publish plugin), e.g., org.jacodb:jacodb-core
• The version for snapshots is generated of the form <date>+<commit>, e.g., 20250730+7c57f265.
• GHA workflow uses the latest JDK 21. It is the project's responsibility to setup itself such that it guarantees the compatibility with Java 8 consumers of built JARs.
• Action gradle/actions/setup-gradle does not have cache setup. By default, it is turned off (read-only) on all branches except main, so we are not going to have any caching for these snapshot releases on neo. See https://github.com/gradle/actions/blob/main/docs/setup-gradle.md#using-the-cache-read-only.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 69.82%. Comparing base (5c8f0eb) to head (7aeb3ed).

Additional details and impacted files

@@            Coverage Diff            @@
##                neo     #335   +/-   ##
=========================================
  Coverage     69.82%   69.82%           
  Complexity     2491     2491           
=========================================
  Files           275      275           
  Lines         15556    15556           
  Branches       2342     2342           
=========================================
  Hits          10862    10862           
  Misses         3768     3768           
  Partials        926      926           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[github-actions]

Test Results

  215 files  ±0    215 suites  ±0   15m 59s ⏱️ -4s
  711 tests ±0    699 ✅ ±0  12 💤 ±0  0 ❌ ±0 
1 977 runs  ±0  1 927 ✅ ±0  50 💤 ±0  0 ❌ ±0 

Results for commit 7aeb3ed. ± Comparison against base commit 5c8f0eb.