minor(test): strengthen bitwise sort-merge join spill coverage

[buraksenn]

Which issue does this PR close?

• Part of Improve test coverage for spilling (memory-limited) sort/aggregation/sort-merge-join #13431

Rationale for this change

Continuing the work after #23988 and #24056. BitwiseSortMergeJoinStream (filtered semi/anti/mark joins) buffers the inner key group and spills it under memory pressure, but existing tests only cover the successful spill path:

• when the memory pool is exhausted and disk spilling is disabled, the error path had no coverage
• the multi-spill slice retention regression test only asserted the semi join outcome; a dropped slice resurrects the anti row and flips mark to false, which row counts alone cannot catch
• no spill test exercised NullEqualsNull, so NULL-key group boundary detection through the spill path was untested

What changes are included in this PR?

• new bitwise_filtered_no_spill: all six semi/anti/mark join types must surface a clear "Disk spilling disabled" error (not spill or panic) when the pool is exhausted with the DiskManager disabled
• extend bitwise_multi_spill_inner_key_group over LeftAnti/LeftMark, asserting the mark column value
• new bitwise_spill_null_key_group: under NullEqualsNull, a NULL-key group spanning a batch boundary must spill as one group with one spill file and match a NULL-key outer row
• extract shared setup of bitwise_spill_with_filter into a fixture

Are these changes tested?

test only change and it can be tested via:

cargo test -p datafusion-physical-plan --lib -- sort_merge_join::tests::bitwise

Are there any user-facing changes?

no test only change

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.17%. Comparing base (e76f1af) to head (de81e38).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #24192      +/-   ##
==========================================
- Coverage   81.17%   81.17%   -0.01%     
==========================================
  Files        1109     1109              
  Lines      388033   388033              
  Branches   388033   388033              
==========================================
- Hits       314992   314985       -7     
- Misses      54501    54507       +6     
- Partials    18540    18541       +1     

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[saadtajwar]

Nice! Not a maintainer but these changes make sense and LGTM :)