feat(python): AssumeRole support for AWS Credential Provider

[nameexhaustion]

Adds support for using an assumed role to CredentialProviderAWS

pl.scan_parquet(
    "s3://.../...",
    credential_provider=pl.CredentialProviderAWS(
        assume_role={
            "RoleArn": "arn:aws:iam::0000000:role/ExampleRole",
            "RoleSessionName": "example",
        }
    ),
)

ref #18979
ref #15838

[nameexhaustion]

refactored to remove the exhaustive cloud-type identification - we only need AWS and GCP for now

also more efficient to use these functions directly as we avoid double-matching

[nameexhaustion]

drive-by - in case a future version of google auth adds timezone info

[codecov]

Codecov Report

Attention: Patch coverage is 58.97436% with 16 lines in your changes missing coverage. Please review.

Project coverage is 80.23%. Comparing base (08732c4) to head (63dd0c0).
Report is 21 commits behind head on main.

Files with missing lines	Patch %	Lines
py-polars/polars/io/cloud/credential_provider.py	53.12%	13 Missing and 2 partials ⚠️
py-polars/polars/io/cloud/_utils.py	85.71%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #19346      +/-   ##
==========================================
+ Coverage   80.21%   80.23%   +0.01%     
==========================================
  Files        1523     1523              
  Lines      209544   209579      +35     
  Branches     2434     2430       -4     
==========================================
+ Hits       168096   168148      +52     
+ Misses      40893    40878      -15     
+ Partials      555      553       -2     

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