fix: update Sonatype OSSRH URL and upgrade GitHub Actions to v4

[mala-emnify]

• pom.xml: legacy OSSRH (s01.oss.sonatype.org) is retired and 404s — point nexusUrl at the compatibility endpoint ossrh-staging-api.central.sonatype.com so releases publish again.
• sonar.yaml: actions/cache@v1 is hard-failed by GitHub — bump cache v1→v4, setup-java v1→v4 (adds now-required distribution: temurin), checkout v2→v4.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.08%. Comparing base (2d38358) to head (1fe7e86).

Additional details and impacted files

@@            Coverage Diff            @@
##               main      #13   +/-   ##
=========================================
  Coverage     81.08%   81.08%           
  Complexity       89       89           
=========================================
  Files            23       23           
  Lines           370      370           
  Branches         35       35           
=========================================
  Hits            300      300           
  Misses           40       40           
  Partials         30       30           

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