Implementation classes named in table properties are imported and instantiated without a type check

[sungwy]

Three properties name a class that PyIceberg imports and calls:

Property	Resolved by	Called as
py-io-impl	_import_file_io (pyiceberg/io/__init__.py)	class_(properties)
write.py-location-provider.impl	_import_location_provider (pyiceberg/table/locations.py)	class_(table_location, table_properties)
s3.retry-strategy-impl	_import_retry_strategy (pyiceberg/io/pyarrow.py)	class_()

Each follows the same pattern:

module = importlib.import_module(module_name)
class_ = getattr(module, class_name)
return class_(...)

None of the three checks that the resolved object is the type it is about to be used as — there is no issubclass against FileIO, LocationProvider, or S3RetryStrategy. Any importable dotted name resolves and is called, with the property map passed as an argument in two of the three cases.

All three properties are read from the merged table property map, so their values can originate in a table's metadata rather than in the operator's catalog configuration.

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Issue investigation generated via claude, reviewed by Sung, Kevin, Fokko.