fix(python): Remove default red formatting for negative floats in write_excel

[mcrumiller]

Closes #17624 if it's accepted. @alexander-beedie.

Quick check as this isn't really worth testing:

from datetime import date

import polars as pl

# Create a Pandas dataframe with some sample data.
df = pl.DataFrame(
    {
        "Dates": [date(2023, 1, 1), date(2023, 1, 2), date(2023, 1, 3)],
        "Strings": ["Alice", "Bob", "Carol"],
        "Numbers": [0.12345, 100, -99.523],
    }
)

df.write_excel(workbook="polars_format_default.xlsx")

Result:

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 80.69%. Comparing base (8bad2fd) to head (2557cb2).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #17646      +/-   ##
==========================================
- Coverage   80.69%   80.69%   -0.01%     
==========================================
  Files        1485     1485              
  Lines      195485   195485              
  Branches     2782     2782              
==========================================
- Hits       157747   157745       -2     
- Misses      37226    37228       +2     
  Partials      512      512              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[alexander-beedie]

I've just closed the linked Issue as "not planned" - we should have sensible/useful default formatting. It's a nice balance of minimal/clean, and actually helpful.

Red is the default colour for negative values in all of Excel's default styles (the ones that actually apply a colour), so this is consistent with expectations/experience 👍

It's also already simple to strip the default formatting in favour of "General" if that's what somebody really wants (for most users it isn't 🙃):

df.write_excel(column_formats={cs.all(): "General"})
df.write_excel(column_formats={cs.numeric(): "General"})