refactor: Unify get_current_checkpoint_from_pipeline helper

[libvarun]

Summary of changes:

1. Refactor: Moved get_current_checkpoint_from_pipeline to metadata-ingestion/src/datahub/testing/state_helpers.py to allow sharing between test suites.
2. Cleanup: Removed duplicate implementation from smoke-test/tests/test_stateful_ingestion.py and updated metadata-ingestion tests to use the shared helper.
3. Verification: Ran smoke-test and relevant unit tests locally, and they passed.

No Deps changed.

[deepgarg760]

@libvarun , linting please

[deepgarg760]

LGTM!!

[libvarun]

@deepgarg760 Please check now. linting issues could be IDE warnings only - the actual project linting passes. Your IDE's Python interpreter isn't pointing to the virtual environment.

[codecov[bot]]

Codecov Report

:white_check_mark: All modified and coverable lines are covered by tests.

:loudspeaker: Thoughts on this report? Let us know!

[codecov[bot]]

Bundle Report

Changes will decrease total bundle size by 2.51MB (-8.02%) :arrow_down:. This is within the configured threshold :white_check_mark:

Detailed changes

Bundle name	Size	Change
datahub-react-web-esm	28.77MB	-2.51MB (-8.02%) :arrow_down:

Affected Assets, Files, and Routes:

view changes for bundle: datahub-react-web-esm

Assets Changed:

Asset Name	Size Change	Total Size	Change (%)
assets/index-*.js	-103.28kB	19.14MB	-0.54%
~~assets/signup-*.mp4~~ (Deleted)	-2.26MB	0 bytes	-100.0% :wastebasket:
~~assets/airflowlogo-*.png~~ (Deleted)	-37.61kB	0 bytes	-100.0% :wastebasket:
~~assets/prestologo-*.png~~ (Deleted)	-33.55kB	0 bytes	-100.0% :wastebasket:
~~assets/sagemakerlogo-*.png~~ (Deleted)	-17.81kB	0 bytes	-100.0% :wastebasket:
~~assets/iceberglogo-*.png~~ (Deleted)	-17.61kB	0 bytes	-100.0% :wastebasket:
~~assets/s3logo-*.png~~ (Deleted)	-16.96kB	0 bytes	-100.0% :wastebasket:
~~assets/sparklogo-*.png~~ (Deleted)	-16.15kB	0 bytes	-100.0% :wastebasket:
~~assets/dagsterlogo-*.svg~~ (Deleted)	-5.45kB	0 bytes	-100.0% :wastebasket: