Implement Async Schema Registry client

[rohitsanj]

What

• Converted the existing sync Schema Registry clients to be made async and placed them in the _async module.
• The code was converted such that it could be made sync by simply applying some regular expression driven replace logic (like await func(x, y, z) -> func(x, y, z), AsyncXYZ -> XYZ and so on). Going forward, all diffs must be solely made to the _async module, the sync clients will be derived from the async clients.
• The same treatment is applied to the tests, any new async test written must work with async keywords removed.

#1971 must be merged before this one.

unasync.py script

Scenario 1: When changes are made to the _async directory but not to its _sync counterpart:

$ python tools/unasync.py --check

⚠️  Detected changes to a _sync directory that are uncommitted.

Files with differences:
  - src/confluent_kafka/schema_registry/_sync/serde.py

Please either:
1. Commit the changes in the generated _sync files, or
2. Revert the changes in the original _async files

Scenario 2: When changes across _async and _sync are consistent.

$ python tools/unasync.py --check

✅ All _sync directories are up to date!

---

Checklist

• Contains customer facing changes? Including API/behavior changes
• Did you add sufficient unit test and/or integration test coverage for this PR?
  • If not, please explain why it is not required

References

JIRA:

Test & Review

Open questions / Follow-ups

[confluent-cla-assistant]

🎉 All Contributor License Agreements have been signed. Ready to merge.
_{Please push an empty commit if you would like to re-run the checks to verify CLA status for all contributors.}

[rohitsanj]

Async implementation of the Kafka consumer -- used only in tests and not surfaced as a public API.

[rohitsanj]

Async implementation of the Kafka producer -- used only in tests and not surfaced as a public API.

[rohitsanj]

With @asyncinit in async files replaced with an empty string in the sync files, this leaves three empty lines separating the classes which is a flake8 violation.

[rayokota]

Thanks @rohitsanj , LGTM

The base branch was changed.

[sonarqube-confluent]

• 51.40% Coverage on New Code (is less than 80.00%)

Analysis Details

53 Issues

• 0 Bugs
• 3 Vulnerabilities
• 50 Code Smells

Coverage and Duplications

• 51.40% Coverage (60.50% Estimated after merge)
• No duplication information (6.20% Estimated after merge)

Project ID: confluent-kafka-python

View in SonarQube

[rayokota]

LGTM

[rohitsanj]

Remove this because it's wrong -- poll(0) could block.