build(pmd): update PMD rules and fix issues

[skaldarnar]

Contains

Updated and customized rules for PMD, adjusted for the launcher project.

All issues have been adressed such that we no longer ignore PMD errors and instead will fail a build if new issues occur.

• build(pmd): use custom PDM rules for the launcher
• build(pmd): adjust custom rules

How to test

Run the PMD checks locally via

gradlew pmdMain
gradlew pmdTest

Run the CheckStyle checks locally via

gradlew checkstyleMain
gradlew checkstyleTest

Or run everything at once via

gradlew check -x test

Outstanding before merging

• [x] fix reported PMD issues or suppress warnings
• [x] fix reported CheckStyle issues or suppress warnings