fix(python): Improve default write_excel int/float format when using a dark "table_style"

[alexander-beedie]

Much better default output when given a "dark" table_style:

Example

import polars as pl

df = pl.DataFrame({
    "dtm": [date(2023, 1, 1), date(2023, 1, 2), date(2023, 1, 3)],
    "str": ["xxx", "yyy", "xxx"],
    "val": [100.5, 55.0, -99.5],
})

df.write_excel(
    workbook="output.xlsx",
    table_style="Table Style Dark 2",
    column_totals=True,
    autofit=True,
)

Before:

Numeric formatting does not look good with dark styles -

After:

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 80.48%. Comparing base (3016c07) to head (90faf67).

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #17869   +/-   ##
=======================================
  Coverage   80.47%   80.48%           
=======================================
  Files        1505     1505           
  Lines      197273   197278    +5     
  Branches     2807     2808    +1     
=======================================
+ Hits       158764   158776   +12     
+ Misses      37987    37980    -7     
  Partials      522      522           

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