NIFI-12857 Add test for and refactor implementation of QueuePrioritizer

[EndzeitBegins]

Summary

Adds test for and refactors implementation of QueuePrioritizer.

NIFI-12857

Additionally, removed some dead code from TestStandardFlowFileQueue.

Tracking

Please complete the following tracking steps prior to pull request creation.

Issue Tracking

• [x] Apache NiFi Jira issue created

Pull Request Tracking

• [x] Pull Request title starts with Apache NiFi Jira issue number, such as NIFI-00000
• [x] Pull Request commit message starts with Apache NiFi Jira issue number, as such NIFI-00000

Pull Request Formatting

• [x] Pull Request based on current revision of the main branch
• [x] Pull Request refers to a feature branch with one commit containing changes

Verification

Please indicate the verification steps performed prior to pull request creation.

Build

• [x] Build completed using mvn clean install -P contrib-check
  • [x] JDK 21

Licensing

• [x] New dependencies are compatible with the Apache License 2.0 according to the License Policy
• [x] New dependencies are documented in applicable LICENSE and NOTICE files

Documentation

• [x] Documentation formatting appears as expected in rendered files