implement and test mean

[flying-sheep]

Fixes #43

other than the scanpy impl, this uses our sum always to also work on e.g. sparse.

IDK what’s up with these CodSpeed regressions/improvements, these two benchmarks (only) seem to be super flaky

[codecov]

Codecov Report

Attention: Patch coverage is 95.65217% with 1 line in your changes missing coverage. Please review.

Project coverage is 95.05%. Comparing base (bdae03a) to head (47a02ff).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/fast_array_utils/stats/_mean.py	90.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #44      +/-   ##
==========================================
- Coverage   95.32%   95.05%   -0.27%     
==========================================
  Files          11       12       +1     
  Lines         171      182      +11     
==========================================
+ Hits          163      173      +10     
- Misses          8        9       +1     

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[codspeed-hq]

CodSpeed Performance Report

Merging #44 will not alter performance

_{Comparing pa/mean (47a02ff) with main (bdae03a)}

Summary

✅ 52 untouched benchmarks
🆕 18 new benchmarks

Benchmarks breakdown

	Benchmark	BASE	HEAD	Change
🆕	test_stats_benchmark[0-numpy.ndarray-float32-mean]	N/A	173.8 µs	N/A
🆕	test_stats_benchmark[0-numpy.ndarray-float64-mean]	N/A	198.7 µs	N/A
🆕	test_stats_benchmark[0-scipy.sparse.csc_array-float32-mean]	N/A	362.3 µs	N/A
🆕	test_stats_benchmark[0-scipy.sparse.csc_array-float64-mean]	N/A	381.3 µs	N/A
🆕	test_stats_benchmark[0-scipy.sparse.csr_array-float32-mean]	N/A	446.4 µs	N/A
🆕	test_stats_benchmark[0-scipy.sparse.csr_array-float64-mean]	N/A	467 µs	N/A
🆕	test_stats_benchmark[1-numpy.ndarray-float32-mean]	N/A	177.2 µs	N/A
🆕	test_stats_benchmark[1-numpy.ndarray-float64-mean]	N/A	195 µs	N/A
🆕	test_stats_benchmark[1-scipy.sparse.csc_array-float32-mean]	N/A	328.4 µs	N/A
🆕	test_stats_benchmark[1-scipy.sparse.csc_array-float64-mean]	N/A	353 µs	N/A
🆕	test_stats_benchmark[1-scipy.sparse.csr_array-float32-mean]	N/A	353.7 µs	N/A
🆕	test_stats_benchmark[1-scipy.sparse.csr_array-float64-mean]	N/A	386.9 µs	N/A
🆕	test_stats_benchmark[None-numpy.ndarray-float32-mean]	N/A	196.4 µs	N/A
🆕	test_stats_benchmark[None-numpy.ndarray-float64-mean]	N/A	202.4 µs	N/A
🆕	test_stats_benchmark[None-scipy.sparse.csc_array-float32-mean]	N/A	341.1 µs	N/A
🆕	test_stats_benchmark[None-scipy.sparse.csc_array-float64-mean]	N/A	351.9 µs	N/A
🆕	test_stats_benchmark[None-scipy.sparse.csr_array-float32-mean]	N/A	327.6 µs	N/A
🆕	test_stats_benchmark[None-scipy.sparse.csr_array-float64-mean]	N/A	345.6 µs	N/A