Allow enable_exactly_once_delivery for gcpubsub

[tungntpham]

This option will ensure no duplication for delivered messages. Redelivery is still possible if the acknowledgement deadline expires.

[Copilot]

Pull request overview

This PR adds support for exactly-once delivery in GCP Pub/Sub subscriptions through a new enable_exactly_once_delivery transport option. When enabled, Google Cloud Pub/Sub provides message deduplication to prevent duplicate message delivery, though redelivery can still occur if the acknowledgment deadline expires.

Key Changes

• Added enable_exactly_once_delivery boolean transport option (defaults to False)
• Updated subscription creation to include the exactly-once delivery setting
• Added comprehensive tests for the new feature

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
kombu/transport/gcpubsub.py	Added documentation, default constant, cached property, and integration into subscription creation; includes incidental quote style normalization in request dict
t/unit/transport/test_gcpubsub.py	Added PropertyMock import and two parameterized tests to verify property behavior and subscription creation with the new setting

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.19%. Comparing base (4055fa7) to head (4924df5).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2431   +/-   ##
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  Coverage   81.19%   81.19%           
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  Files          77       77           
  Lines        9735     9739    +4     
  Branches     1098     1098           
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+ Hits         7904     7908    +4     
  Misses       1625     1625           
  Partials      206      206           

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