Fix pyright issues and improve type safety in Dagster Delta

[ismailtsdln]

Bug Fixes

• Fixed a potential PossiblyUnboundVariable issue in base.py by initializing partition_filters at the beginning of the handle_output method.

Type Safety Improvements

• Aligned method signatures of _DeltaLakePyArrowTypeHandler and _DeltaLakePolarsTypeHandler with the base class DeltalakeBaseArrowTypeHandler.

This resolves Pyright errors caused by incompatible method overrides.

• Added Pyright ignore directives for legacy Dagster import paths that are still required for backward compatibility.

• This prevents false-positive static analysis errors when running against newer Dagster versions.

Verification Tests

Ran the full test suite; all tests passed successfully (55/55):

uv run pytest libraries/dagster-delta/dagster_delta_tests

Static Analysis

Ran Pyright across the entire repository with zero reported errors:

uv run pyright .

[gfvioli]

I was just about to implement a couple of the same fixes in another PR, but pull them out to make it on this one.

I'll finish review after #51 is merged to avoid the upcoming merge conflict, if it runs on my local then I'll approve too.

[gfvioli]

@ismailtsdln also fell free to send me a PR to my branch so I push this in one go with the new release!