Configure the confluent:// transport from app settings via kafkaesq

[wbarnha]

Switching a Faust app between the kafka:// (aiokafka) and confluent://
(librdkafka) transports meant losing most of its configuration: the
confluent driver translated seven settings by hand and ignored
broker_credentials entirely, so an app with SASL simply connected as
plaintext.

Add kafkaesq as an optional dependency -- pip install
"faust-streaming[kafkaesq]" -- and put it to work in both directions in the
new faust.transport.kafkaesq module:

• app_settings_to_confluent derives a librdkafka config from app settings,
  which the confluent driver now uses for its consumers and producer. With
  the extra installed the full settings table is translated; without it the
  driver falls back to the mapping it always had, so the extra is genuinely
  optional.
• confluent_to_app_settings goes the other way, turning an existing
  librdkafka config into faust.App arguments.
• credentials_to_confluent / credentials_from_confluent convert
  broker_credentials to and from librdkafka security keys, which kafkaesq
  leaves alone because Faust configures authentication with a runtime
  object.

Three things the driver got wrong, found by feeding the generated configs to
real confluent_kafka clients (a new test does this, since a mocked-out
client cannot reject a key):

• consumer_max_fetch_size was sent as fetch.max.bytes, which bounds the whole
  fetch response rather than one partition; aiokafka's equivalent is
  max.partition.fetch.bytes.
• A client-only app built a consumer with no group.id, which librdkafka
  refuses outright. It now gets a group of its own, so it still cannot
  disturb the worker group.
• producer_request_timeout defaults to 20 minutes, above librdkafka's
  15-minute ceiling for request.timeout.ms, which fails client construction.
  Values are clamped into librdkafka's ranges, with a warning.

The consumer no longer sends request.timeout.ms, a producer-only property
librdkafka warns about and ignores, and the deprecated default.topic.config
wrapper is gone -- auto.offset.reset is a top-level key now, and follows
consumer_auto_offset_reset instead of always being "earliest".

Co-Authored-By: Claude Opus 5 noreply@anthropic.com
Claude-Session: https://claude.ai/code/session_01BYhhm6H1FQskUmDqjrft7G

[codecov]

Codecov Report

❌ Patch coverage is 95.83333% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 96.07%. Comparing base (4af976b) to head (d80875d).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
faust/transport/kafkaesq.py	95.83%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #761      +/-   ##
==========================================
+ Coverage   96.06%   96.07%   +0.01%     
==========================================
  Files         103      104       +1     
  Lines       11072    11153      +81     
  Branches     1191     1196       +5     
==========================================
+ Hits        10636    10715      +79     
  Misses        345      345              
- Partials       91       93       +2     

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