[TPU Raiden] Fix [Failure/ReceiveDisconnect]: propagate broken inbound streams to fail active receive sessions and release staging slots immediately.

[copybara-service]

[TPU Raiden] Fix [Failure/ReceiveDisconnect]: propagate broken inbound streams to fail active receive sessions and release staging slots immediately.

When an inbound TCP push connection fails, resets, or suffers an I/O read error,
the transport server previously logged the error but did not notify the owning delegate.
Without this notification, decode receive sessions remained oblivious to the disconnect
and stalled until per-transfer timeouts (30s) expired, keeping host staging buffers locked
and causing Head-of-Line blocking / slot starvation for subsequent healthy transfers.

This change:

1. Adds OnReceiveFailed to RawBufferTransportDelegate and BlockTransportDelegate.
2. In BlockTransport and RawBufferTransport, invokes OnReceiveFailed(uuid, status)
   whenever an incoming push stream fails.
3. Wires OnReceiveFailed through KVCacheManagerBase's TransferEventHooks to
   KVCacheManagerWithTransfer::OnReceiveFailed.
4. In KVCacheManagerWithTransfer::OnReceiveFailed, immediately finishes the active
   receive session with the error status, setting draining=true and releasing
   host staging slots back to the free pool immediately on socket disconnect.
5. Adds unit tests in block_transport_test and kv_cache_manager_with_transfer_test
   verifying immediate failure notification and receive session settlement.

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