Speed up and re-enable (un-`@Nightly`) tests

### Description

See #15212 for background.

The "long tail" of slowest tests was marked `@Nightly` with a comment of `// incredibly slow` or similar with 5 commits:
* https://github.com/apache/lucene/commit/86160952d9f2908f440c6d2327790f2309aea425
* https://github.com/apache/lucene/commit/c3ef12f829285da4ac83cd97ba9f5003e7be1510
* https://github.com/apache/lucene/commit/6c66a9d0ea9b4cde99accc832d6d998512c1f928
* https://github.com/apache/lucene/commit/1aa9ed3f379c12de6cf5c26f35f02ee259e25a8a
* https://github.com/apache/lucene/commit/7a663d68f1b2a71b309857fe49ddaf19f316ce5f

This is not ideal: just a workaround to help keep the CI going. Instead we would prefer tests run quickly so that they can e.g. run when testing new PRs.

We should fix the performance issues with these tests if possible. Maybe some truly need to remain `@Nightly`, but it should be the last resort. In many cases, the test might just be slow "some of the time" or consume too many resources (threads). For example, multithreaded cases using more than 2 threads: it should not be needed. Other tests might be using too much data/memory/cpu cycles and just need to be toned down. Other ones might even be real performance issues, we have to look into them more to figure out.

Feel free to open issue/PR for any of these tests if you have an idea how to fix them.

Start with the background in #15212, then inspect the five commits listed in the issue and the tests marked @Nightly or commented as incredibly slow. Identify whether each test is slow intermittently or consumes excessive threads, data, memory, or CPU. Done means improving the relevant tests enough to re-enable them where possible, while retaining @Nightly only when justified.

Written by the indexing model from the issue text.