Log an error when an exception bypasses the dead letter queue

[nabisobhi]

Stacked on #353 — please review that one first. This PR''s diff is against nabisobhi-bookish-waddle, so it shows only the logging change.

Why

#353 lets registered exception types bypass the dead letter queue and propagate, crashing the consumer. Until now that happened silently from the Consumer''s point of view — there was no record of why the consumer died or which message triggered it.

Change

Consumer now takes an optional ILogger<Consumer> (defaulting to NullLogger<Consumer>.Instance, so existing call sites and tests are unaffected) and logs before rethrowing:

Exception of type {ExceptionType} bypassed the dead letter queue for message with key {Key} from topic {SourceTopic}. Failing the consumer

Logged at Error level with the exception attached. The real logger is resolved in both AddConsumer overloads.

To log at that point, the bypass check moved out of the exception filter into the catch body, which now rethrows with a bare throw;. That preserves the original stack trace, and behavior is otherwise identical.

Overlap worth a reviewer''s opinion

ConsumerHostedService.ConsumeAll already logs any escaping exception as "Unhandled error occurred while consuming messaging", so a bypassed exception will now produce two Error entries: this context-rich one, then the generic boundary one. That''s a common pattern (detail at the site, generic at the boundary), but if you''d rather avoid the duplication, options are to drop this to Warning or skip this PR entirely — #353 is fully functional without it.

Notes

• No new NuGet dependencies; Microsoft.Extensions.Logging.Abstractions is already referenced.
• No public API change — Consumer is internal.
• Added LoggerSpy<T> test double rather than Mock<ILogger<Consumer>>, because Moq can''t proxy a generic closed over an internal type without InternalsVisibleTo("DynamicProxyGenAssembly2").

Tests

Two new tests: the bypass logs the expected level/exception/message, and dead-lettered messages do not log the bypass error. TestConsumer 37/37, full suite 156/156, build clean with 0 warnings.