fix: strip path root correctly in partition extraction

[hsusul]

Feature or Bugfix

• Bugfix

Detail

• Fix _extract_partitions_from_path in awswrangler/_arrow.py where f"{path_root}/" was evaluated on a path_root variable that was already normalized to end with a trailing slash (/).
• Previously, f"{path_root}/" resulted in a double trailing slash (//), causing path_wo_filename.replace(f"{path_root}/", "") to fail silently and return path_wo_filename unstripped.
• Consequently, if path_root contained any directory or bucket segment with an = (e.g. s3://bucket/env=dev/table/), _extract_partitions_from_path incorrectly parsed env=dev as a dataset partition column ({'env': 'dev', 'year': '2023'} instead of {'year': '2023'}).
• Replaced .replace(...) with removeprefix(...) across partition and copy path resolution functions (_arrow.py, s3/_read.py, s3/_copy.py) to safely strip prefixes without side effects.
• Added comprehensive unit tests in test_utils.py and a moto test in test_moto.py.

Relates

• N/A

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