fix(python): Give priority to pycapsule interface in from_dataframe

[MarcoGorelli]

closes #20316. As in, to clarify:

• The first example in that issue uses pandas numpy types, which don't support missing values, and so there was no possibility of ever round-tripping
• The second example is already fixed with pandas 2.2.2+, but not with 2.2.1. We can't anything about interchange protocol bugs in old pandas versions, but we can use something better than the interchange protocol 😎 With this PR, the second example from the issue passes with pandas 2.2.1. Given that there's possibly millions of people still using pandas pre-2.2.2, I think this is worth fixing

As suggested in #20065 (comment), this gives priority to the pycapsule interface over the interchange protocol. I did the same in pandas: pandas-dev/pandas#60739

"pl.from_dataframe" shows up a scary amount of times in https://github.com/search?q=%22pl.from_dataframe%22&type=code 🥶

[MarcoGorelli]

this no longer raises with allow_copy=False - I don't know how strict (if at all?) the pycapsule interface is about copies, will take a look

[MarcoGorelli]

I checked and none of the examples in https://github.com/search?q=%22pl.from_dataframe%22&type=code use allow_copy=False, so I'm not sure how much we should be concerned?

I'd like to suggest just deprecating the argument tbh

[codecov]

Codecov Report

Attention: Patch coverage is 86.66667% with 2 lines in your changes missing coverage. Please review.

Project coverage is 79.95%. Comparing base (25d83c6) to head (96a6c44).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
py-polars/polars/convert/general.py	86.66%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #21377      +/-   ##
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+ Coverage   79.84%   79.95%   +0.10%     
==========================================
  Files        1597     1597              
  Lines      228911   228956      +45     
  Branches     2618     2621       +3     
==========================================
+ Hits       182785   183051     +266     
+ Misses      45527    45300     -227     
- Partials      599      605       +6     

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[MarcoGorelli]

these tests are very specific to the interchange protocol, so I've kept the test to those (rather than letting the pycapsule interface take precedence)