0.2.19 changes

[norrisjeremy]

• Update to latest Maven (3.9.8), Maven Wrapper (3.3.2) & Java (21.0.3) releases.
• Only execute build once during CI and then run distinct jobs to run tests for each Java version.
  -- This will require changes to the expected checks for PRs.
• Run tests on Java 22.
  -- I'm envisioning we will update this every 6 months to follow the latest Java release.
• Harden CI workflows by pinning action versions to specific commit hashes.
  -- See security hardening recommendations.
• Increase Dependabot open PR limit.
  -- Since there may be a larger volumes of update PRs incoming for GHA workflows now that they are pinned.
• Enforce DHGEX prime modulus bit length meets configured constraints
  -- This should match OpenSSH behavior, as seen here.