fix: benchmark timeout for too much outer joins on concat

[ilan-gold]

See https://github.com/scverse/anndata/actions/runs/24782425669/job/72516966006?pr=2407 where we were timing out

• Closes #
• Tests added

• Release note not necessary because: dev change

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.48%. Comparing base (91b6289) to head (df3b7a3).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2408      +/-   ##
==========================================
- Coverage   87.43%   85.48%   -1.96%     
==========================================
  Files          49       49              
  Lines        7728     7728              
==========================================
- Hits         6757     6606     -151     
- Misses        971     1122     +151     

see 8 files with indirect coverage changes

[scverse-benchmark]

Benchmark changes

Change	Before [91b6289]	After [df3b7a3]	Ratio	Benchmark (Parameter)
-	5.93±0.08ms	5.09±0.1ms	0.86	dataset2d.Dataset2D.time_full_to_memory('h5ad', (-1,), 'numeric')
+	12.3±2ms	15.3±0.1ms	1.24	dataset2d.Dataset2D.time_getitem_slice('zarr', None, 'cat')
+	8.0234375	9.0234375	1.12	readwrite.H5ADWriteSuite.track_peakmem_write_compressed('pbmc3k')

Comparison: https://github.com/scverse/anndata/compare/91b6289dde5037165ecf9412118497b7f8b21088..df3b7a34f376796d9c0381cde5cdf6cfddc75eb3
Last changed: Wed, 22 Apr 2026 17:23:06 +0000

More details: https://github.com/scverse/anndata/pull/2408/checks?check_run_id=72544679470