check duplicate exclusion cases in ProblemList files

If there are more exclusion entries for same testcase only the last occurrence takes effects even if each entry has different tracked issue or different os-arch.

Testcase excluded by multiple lines happened quite a few times which causes confusion and wastes efforts to triage.

We should check ProblemList files for this to ensure no multiple entries is added, especially when PR is adding the new entry.

The main script for problemlist check is https://github.com/adoptium/aqa-tests/blob/master/scripts/disabled_tests/exclude_parser.py

https://github.com/adoptium/aqa-tests/pull/5863#issuecomment-2595798908

Review scripts/disabled_tests/exclude_parser.py and the referenced ProblemList files; begin by tracing how repeated testcase exclusions are parsed. Done means the check identifies multiple entries for the same testcase, including entries with different tracked issues or os-arch values, so duplicate additions can be caught.

Written by the indexing model from the issue text.