feat(python): Load AWS endpoint_url using boto3

[nameexhaustion]

• Fixes inconsistent usage of AWS endpoint URL #21784
• Fixes Scan Parquet not reading aws config to infer storage option endpoint_url #18420

Note, this will require boto3 to be installed on the system that executes the query. It is not compatible with:

• Passing a custom credential provider to credential_provider (or passing None)

[nameexhaustion]

drive-by, ensure eprint does not capture sys.stderr upon import, this caused pytest capfd to not work as it presumably relies on patching sys.stderr (pytest-dev/pytest#5997)

[codecov]

Codecov Report

Attention: Patch coverage is 80.18018% with 22 lines in your changes missing coverage. Please review.

Project coverage is 81.04%. Comparing base (80e1e53) to head (1a00a38).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/polars-io/src/cloud/options.rs	78.04%	9 Missing ⚠️
crates/polars-io/src/cloud/credential_provider.rs	78.78%	7 Missing ⚠️
.../polars/io/cloud/credential_provider/_providers.py	79.31%	5 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #22851      +/-   ##
==========================================
+ Coverage   80.98%   81.04%   +0.05%     
==========================================
  Files        1674     1674              
  Lines      236937   237065     +128     
  Branches     2787     2792       +5     
==========================================
+ Hits       191883   192127     +244     
+ Misses      44388    44269     -119     
- Partials      666      669       +3     

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

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.