[MASSEMBLY-970] Deduplicate artifact filter patterns

[wilx]

Summary

Deduplicate identical artifact-filter criteria before compiling them into internal pattern objects.

Each occurrence was previously compiled into a distinct object whose equality is identity-based. Matching stops after the first matching pattern, so an identical second object remained untriggered. In Maven Assembly Plugin this produced a false "patterns were never triggered" warning and caused assemblies using strict filtering to fail.

The regression test exercises both inclusion and exclusion filters through their shared statistics-reporting contract.

Fixes apache/maven-assembly-plugin#1178

Validation

• Verified that the new regression test fails for both filters before the runtime change.
• JAVA_HOME=/opt/jdks/latest-8 /opt/maven/apache-maven-3.6.3/bin/mvn -DminimalMavenBuildVersion=3.6.3 clean verify -e
• JAVA_HOME=/opt/jdks/latest-21 /opt/maven/latest/bin/mvn clean verify -e
• JAVA_HOME=/opt/jdks/latest-21 /opt/maven/latest-4/bin/mvn clean verify -e
• Ran the original Maven Assembly reproducer with Assembly Plugin 3.8.1-SNAPSHOT and this patched library, using both normal and strict filtering under Maven 3.9.16 and Maven 4.0.0-rc-5. All four builds passed without the false warning, and each archive contained the expected single Jython JAR.

Following this checklist to help us incorporate your
contribution quickly and easily:

• Your pull request should address just one issue, without pulling in other changes.
• Write a pull request description that is detailed enough to understand what the pull request does, how, and why.
• Each commit in the pull request should have a meaningful subject line and body.
  Note that commits might be squashed by a maintainer on merge.
• Write unit tests that match behavioral changes, where the tests fail if the changes to the runtime are not applied.
  This may not always be possible but is a best-practice.
• Run mvn verify to make sure basic checks pass.
  A more thorough check will be performed on your pull request automatically.
• You have run the integration tests successfully (mvn -Prun-its verify).
  This repository does not define a run-its profile; the downstream Assembly reproducer was run directly as described above.

If your pull request is about ~20 lines of code you don't need to sign an
Individual Contributor License Agreement if you are unsure
please ask on the developers list.

To make clear that you license your contribution under
the Apache License Version 2.0, January 2004
you have to acknowledge this by using the following check-box.

• I hereby declare this contribution to be licenced under the Apache License Version 2.0, January 2004
• In any other case, please file an Apache Individual Contributor License Agreement.