feat(python)!: Support decimals by default when converting from Arrow

[stinodego]

Closes #15152

Changes

• Update conversion from Arrow to always convert Decimals into Polars Decimals, rather than cast to Float64.
• Deprecate Config.activate_decimals

Example

Before

>>> from decimal import Decimal as D
>>> import pyarrow as pa
>>> arr = pa.array([D("1.01"), D("2.25")])
>>> pl.from_arrow(arr)
shape: (2,)
Series: '' [f64]
[
        1.01
        2.25
]

After

>>> pl.from_arrow(arr)
shape: (2,)
Series: '' [decimal[3,2]]
[
        1.01
        2.25
]

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.35%. Comparing base (2de5764) to head (d39a9a8).
Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #15324      +/-   ##
==========================================
- Coverage   81.36%   81.35%   -0.01%     
==========================================
  Files        1364     1364              
  Lines      176615   176588      -27     
  Branches     2526     2524       -2     
==========================================
- Hits       143696   143668      -28     
- Misses      32435    32437       +2     
+ Partials      484      483       -1     

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[JulianCologne]

nice! This would also resolve #15152