fix: remove mamba backend for asv

[ilan-gold]

• See [BUG] Kill libmambapy airspeed-velocity/asv#1525
• Tests added
• Release note added (or unnecessary)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 66.64%. Comparing base (e3a6376) to head (49c3148).
⚠️ Report is 54 commits behind head on main.

❌ Your project status has failed because the head coverage (66.64%) is below the target coverage (80.00%). You can increase the head coverage or adjust the target coverage.

❗ There is a different number of reports uploaded between BASE (e3a6376) and HEAD (49c3148). Click for more details.

HEAD has 3 uploads less than BASE

Flag	BASE (e3a6376)	HEAD (49c3148)
	5	2

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #2129       +/-   ##
===========================================
- Coverage   84.48%   66.64%   -17.85%     
===========================================
  Files          46       46               
  Lines        7078     7078               
===========================================
- Hits         5980     4717     -1263     
- Misses       1098     2361     +1263     

see 27 files with indirect coverage changes

[scverse-benchmark]

Benchmark changes

Change	Before [e3a6376]	After [49c3148]	Ratio	Benchmark (Parameter)
+	9.95±0.09ms	12.5±0.3ms	1.26	dataset2d.Dataset2D.time_getitem_slice(<function Dataset2D.> (0), (-1,))
-	322±10μs	289±6μs	0.9	sparse_dataset.SparseCSRContiguousSlice.time_getitem_adata((10000, 10000), 'alternating', False)

Comparison: https://github.com/scverse/anndata/compare/e3a6376af45e01787a4253818ea0eee029e43b69..49c314890a9d081966a7b605e0cfa3dbcad15744
Last changed: Mon, 29 Sep 2025 09:49:02 +0000

More details: https://github.com/scverse/anndata/pull/2129/checks?check_run_id=51475827886