feat(redis-extension): add redis pubsub/streams bridge with tested config and interop coverage

[krital]

Why

A customer is actively using this integration and explicitly requested Redis extension support with configurable behavior, tested examples, and interoperability coverage.

What

• Adds new redis-extension module (Lettuce-based Redis Pub/Sub + Streams bridge)
• Preserves MAPS typed data and headers across Redis envelopes
• Adds CloudEvent wrap support and round-trip harness:
  Redis -> MAPS -> CloudEvent -> MAPS -> Redis
• Adds pull-side stream reconnect and metrics support
• Adds optional stream tuning config with defaults:
  • redis.stream.poll_ms
  • redis.stream.min_poll_ms
  • redis.stream.batch_size
  • redis.stream.pending_sample_every
• Adds tested config examples and Redis extension docs
• Wires module into root pom.xml and top-level README

Validation

• mvn -q -pl redis-extension test
• mvn -q -pl redis-extension -Dsurefire.excludedGroups= -Dgroups=perf test

Notes

Redis Pub/Sub is intentionally treated as an ephemeral signaling/integration layer; core delivery guarantees remain in MAPS.