Type hint __enter__ to return the same object type that called it

[leifwar]

What

Have change the return type hint for both Producer.__enter__() and Consumer.__enter__() to Self. This will make it possible to extend this class through inheritance. Related to #2157.

Checklist

• Contains customer facing changes? Including API/behavior changes
• [x ] 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

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