Add SQS shared-stream producer and trigger

[FrankYang0529]

Adds SqsSharedStreamProducer and SqsSharedStreamTrigger to the Amazon provider, backing the producer-side ack channel for shared-stream triggers (#67523). Many event-driven triggers watching the same SQS queue can now share a single consumer.

How it works

• SqsSharedStreamProducer owns one SQS consumer for a shared-stream group: open_stream receives messages without deleting them and yields (body, SqsBrokerPayload); deletion happens only in advance.
• A background task extends each outstanding message's visibility timeout while it is being processed, so a slow subscriber does not cause SQS to redeliver a message still in flight.
• On advance: acked and rejected messages are deleted (rejected is dropped); failed (ack timeout / overflow) resets visibility to 0 for immediate redelivery; a broadcast no subscriber was online for is left to lapse and be redelivered when a subscriber returns.
• The advance lane is the FIFO MessageGroupId when present, falling back to the receipt handle, so FIFO groups advance in order while standard queues get maximum per-message parallelism.

related: #67523

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Was generative AI tooling used to co-author this PR?

• Yes — Claude Code (Opus 4.8)

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