fix: reject mismatched raw var names in QC metrics

[AkshajKashyap]

• Closes calculate_qc_metrics(use_raw=True) labels .raw's matrix with adata.var #4347
• Tests included
• Release notes not necessary because:

Summary

calculate_qc_metrics(use_raw=True) can select the matrix from .raw while QC masks and variable labels still come from adata.var.

When the two variable axes differ, this can either raise due to a shape mismatch or silently associate QC results with the wrong variables.

This PR takes the conservative approach of requiring adata.raw.var_names and adata.var_names to be identical when use_raw=True. A mismatch now raises before any QC results are written. The same validation applies to describe_obs and describe_var.

Supporting different raw axes would require defining additional alignment and inplace-output semantics, so this PR avoids silently inventing those semantics.

Tests

Regression coverage includes subset and reordered variable axes, return and inplace modes, all three QC entry points, and no partial mutation on failure.

Before: 56 passed, 7 xfailed
After: 68 passed, 7 xfailed

ruff check and ruff format --check pass.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.93%. Comparing base (5f2accb) to head (c884ee2).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff            @@
##           main    #4364       +/-   ##
=========================================
+ Coverage      0   81.93%   +81.93%     
=========================================
  Files         0      134      +134     
  Lines         0    13034    +13034     
=========================================
+ Hits          0    10680    +10680     
- Misses        0     2354     +2354     

Flag	Coverage Δ
hatch-test.low-vers	78.81% <100.00%> (?)
hatch-test.pre	81.80% <100.00%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/scanpy/preprocessing/_qc.py	96.05% <100.00%> (ø)

... and 133 files with indirect coverage changes