Fix sticky handlers executing multiple times with global partitioning

[jeremydmiller]

Closes #2303

Summary

When a message type was configured with both GlobalPartitioned() routes and explicit Publish().ToLocalQueue().AddStickyHandler() routes, sticky handlers executed multiple times per message. The GlobalPartitionedRoute fans out to sticky handler queues via companion local queues, but the explicit local queue routes also delivered to the same queues — causing duplicate execution.

Defense in depth with three fixes:

1. MessageRouter<T>.DeduplicateRoutes() — Primary fix. When a GlobalPartitionedRoute is present, removes explicit local queue routes targeting sticky handler queues since the fanout already delivers to them.

2. GlobalPartitionedRoute.StickyHandlerFanoutUris — Exposes which local queue URIs the fanout targets, enabling deduplication at the router level.

3. FanoutMessageHandler — Safety net. Deduplicates target URIs with a HashSet to prevent double delivery when the same queue is reachable via multiple paths.

Reproduction

A Kafka-based test (sticky_handlers_with_global_partitioning.dual_publish_to_kafka_and_local_sticky_should_not_double_execute) reproduces the exact pattern from the issue:

• Before fix: Handler A=2, Handler B=2 (each executed twice)
• After fix: Handler A=1, Handler B=1 (each executed once)

Test plan

• CoreTests: 1,189 passed, 0 failed
• Kafka reproduction test confirms fix (handlers execute exactly once)
• All Kafka compliance tests pass (54/54)
• Solution compiles cleanly

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