Update Maven wrapper

[fabian-barney]

Summary

• update the Maven wrapper distribution from Maven 3.9.11 to Maven 3.9.15
• use Maven 3.9.15 because the initially targeted 3.9.12 wrapper distribution URL is not available, while 3.9.15 resolves from Maven Central and is the latest stable Maven 3.x distribution found at execution time
• keep existing Java 21 compiler release and dependency/plugin versions unchanged because versions:display-* reports them current

Validation

• ./mvnw.cmd -B -v
• ./mvnw.cmd -B verify -Dcentral.skipPublishing=true

Closes #53

[Copilot]

Pull request overview

Updates the project’s Maven Wrapper to use Maven 3.9.12 for consistent, reproducible builds without changing the Java toolchain or any dependency/plugin versions.

Changes:

• Bumped Maven Wrapper distributionUrl from Maven 3.9.11 to 3.9.12.
• Left wrapper JAR (maven-wrapper 3.3.4) and the rest of the build configuration unchanged.

[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated 1 comment.