fix(cache): redis backend uses async clients + real-redis CI

[wbarnha]

Description

Re-opens #725 onto master. #725 was merged into its stale stacked-parent branch (claude/fix-715-cibuildwheel-314) instead of master, so its content never reached master. This branch is the same commit cherry-picked directly onto master, independent of any chain.

Testing redis in CI surfaced that the redis cache backend was broken against a real server. This fixes it and adds the real-redis CI leg.

The bug (proven against a live redis)

The backend maps schemes to the synchronous redis.StrictRedis / redis.RedisCluster, but _get/_set/_delete/connect await the client:

>>> await app.cache.set("k", b"v", timeout=60)
TypeError: object bool can't be used in 'await' expression

It only ever looked fine because every unit test mocked the client with AsyncMock.

Fix — faust/web/cache/backends/redis.py

• Use the asyncio clients (redis.asyncio.StrictRedis / redis.asyncio.RedisCluster) so the awaited calls are real coroutines. Verified end-to-end against a live redis.
• Close the client on stop (on_stop → await client.aclose()).
• Bind redis = None (not just aredis) on ImportError, so the "not installed" guard raises ImproperlyConfigured instead of NameError.

Tests & CI

• mocked_redis fixture patches redis.asyncio.StrictRedis and provides aclose.
• Test_RedisScheme + the not-installed test re-enabled, asserting the async client wiring.
• New real-redis integration tests (tests/integration/cache/), env-gated on FAUST_TEST_REDIS (skip cleanly when no server is reachable).
• New test-redis-integration job with a redis:7 service container. Advisory (not in the required check gate), matching the Kafka integration job.

Verification

Unit test_cache.py (32) + integration tests/integration/cache (2) → 34 passed; integration tests skip cleanly with no reachable redis; flake8/black/isort clean.

🤖 Generated with Claude Code

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Generated by Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 80.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 94.21%. Comparing base (f77a678) to head (7bde1bd).

Files with missing lines	Patch %	Lines
faust/web/cache/backends/redis.py	80.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #731      +/-   ##
==========================================
+ Coverage   94.18%   94.21%   +0.02%     
==========================================
  Files         104      104              
  Lines       11154    11158       +4     
  Branches     1202     1203       +1     
==========================================
+ Hits        10505    10512       +7     
+ Misses        548      545       -3     
  Partials      101      101              

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