Kafkacrypto

This maintenance releases fixes a number of bugs:

- Fixes the FutureRecordMetadata implementation in confluent_kafka_wrapper to be functional
- Avoid initializing the root logger on package import by switching from logging to warnings in __init__.py
- Added logging and timeout fixes in confluent_kafka_wrapper
- Prevent management thread exits on recoverable errors
- Fix bug that was present in all public versions of Kafkacrypto that prevented direct producer-to-consumer key exchanges without controller interaction.

This version fixes a bug in the new flush implementation in confluent_kafka_wrapper that was necessary to work around an issue in librdkafka. Unfortunately, the original implementation did not respect being multi-threaded safe, and would thus encounter scenarios where flush would never return. Fix that by properly checking the number of messages remaining to be produced, in addition to tracking the number of messages produced within each thread calling poll. Also adds a timeout to all flush calls to reduce the impact of any such related bugs.

This version adds compatibility for Python 3.10, and adds a work-around for a nasty bug in librdkafka 1.8.0 (persists up to at least 1.8.2) that caused an inability to send subscribe messages and (eventually) resulted in memory corruption and a crash of the management thread.

This version adds logging rate limiting for certain messages that can occur at high frequency, and also improves readability of chain information on errors.