enable pulsar flink source to read topics with key hash range

[nlu90]

(If this PR fixes a github issue, please add Fixes #<xyz>.)

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Motivation

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Modifications

Fix https://github.com/streamnative/pulsar-flink/issues/230

Verifying this change

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This change is a trivial rework / code cleanup without any test coverage.

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This change is already covered by existing tests, such as (please describe tests).

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This change added tests and can be verified as follows:

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• Added integration tests for end-to-end deployment with large payloads (10MB)
• Extended integration test for recovery after broker failure

Documentation

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This is a bug fix.

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[github-actions[bot]]

@nlu90:Thanks for your contribution. For this PR, do we need to update docs? (The PR template contains info about doc, which helps others know more about the changes. Can you provide doc-related info in this and future PR descriptions? Thanks)

[github-actions[bot]]

@nlu90:Thanks for providing doc info!