fix: resolve SettingWithCopyWarning in histogram postprocessing

[FrancescoCastaldi]

Summary

Fixes #36530

Replaces direct column assignment on a potentially-sliced DataFrame with an explicit .copy() followed by .loc[:, column] assignment, eliminating the SettingWithCopyWarning that appears in logs on every Histogram chart load.

Before

df[column] = to_numeric(df[column], errors="coerce")

After

df = df.copy()
df.loc[:, column] = to_numeric(df[column], errors="coerce")

Why .copy() + .loc[]?

df.dropna(subset=[column]) (the line immediately above) returns a view or a copy depending on internal pandas state. Calling .copy() explicitly makes ownership unambiguous, which is the pandas-recommended pattern for avoiding SettingWithCopyWarning — and is future-proof for pandas 3.x Copy-on-Write semantics.

Testing

• Verified the warning no longer appears when loading a dashboard containing a Histogram chart
• Existing unit tests in tests/unit_tests/utils/pandas_postprocessing/test_histogram.py pass without modification
• No behavioral change — only log noise removed

Checklist

• Added/updated tests
• Linted with pre-commit hooks (black, isort, pylint, mypy)
• PR title follows the Conventional Commits spec (fix: ...)
• Issue linked via Fixes #36530

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• Files reviewed - 1 · Commit Range: 2c55fe9..2c55fe9

  • superset/utils/pandas_postprocessing/histogram.py
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[codecov]

Codecov Report

❌ Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 64.16%. Comparing base (09a94fa) to head (f56d3d0).

Files with missing lines	Patch %	Lines
superset/utils/pandas_postprocessing/histogram.py	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #40462      +/-   ##
==========================================
- Coverage   64.18%   64.16%   -0.02%     
==========================================
  Files        2592     2592              
  Lines      139271   139272       +1     
  Branches    32337    32337              
==========================================
- Hits        89385    89358      -27     
- Misses      48351    48376      +25     
- Partials     1535     1538       +3     

Flag	Coverage Δ
hive	39.21% <0.00%> (-0.01%)	⬇️
mysql	?
postgres	58.80% <0.00%> (-0.01%)	⬇️
presto	40.89% <0.00%> (-0.01%)	⬇️
python	60.31% <0.00%> (-0.05%)	⬇️
sqlite	58.44% <0.00%> (-0.01%)	⬇️
unit	100.00% <ø> (ø)

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