Support custom id function in async_dofn

[dustin12]

Allow users to specify a custom id function to be used instead of the default hashing function to be used to deduplicate messages. For instance if user has a UID field in their messages they wish to use.

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[gemini-code-assist]

Summary of Changes

Hello @dustin12, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request enhances the AsyncWrapper in Apache Beam's Python SDK by providing users with the flexibility to define a custom function for identifying and deduplicating messages. This is particularly useful in scenarios where the default hashing mechanism might not accurately represent the logical uniqueness of messages, such as when a specific field like a UID should be used for deduplication. The change allows for more precise control over how elements are tracked and processed asynchronously.

Highlights

• Custom ID Function for AsyncWrapper: Introduced an id_fn parameter to the AsyncWrapper constructor, allowing users to specify a custom function for generating unique identifiers for elements. This function defaults to an identity function if not provided.
• Enhanced Deduplication Logic: Modified the internal tracking and deduplication mechanisms within AsyncWrapper (specifically in schedule_if_room and commit_finished_items) to utilize the newly introduced id_fn. This ensures that elements are tracked and deduplicated based on the custom ID rather than their default hash.
• New Test Case for Validation: Added test_custom_id_fn to async_dofn_test.py to thoroughly validate the functionality of the custom ID function. This test demonstrates how elements with different content but the same custom ID are correctly deduplicated.

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[github-actions]

Assigning reviewers:

R: @shunping for label python.

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[github-actions]

The Workflow run is cancelling this PR. It is an earlier duplicate of 2083803 run.

[github-actions]

The Workflow run is cancelling this PR. It is an earlier duplicate of 1729654 run.

[github-actions]

The Workflow run is cancelling this PR. It is an earlier duplicate of 2083803 run.

[github-actions]

The Workflow run is cancelling this PR. It is an earlier duplicate of 1729654 run.

[github-actions]

The Workflow run is cancelling this PR. It is an earlier duplicate of 2083803 run.

[github-actions]

The Workflow run is cancelling this PR. It is an earlier duplicate of 1729654 run.

[shunping]

LGTM