fix(node): recover sync state after outbound request failure

[zjubiology]

Description

Fix a sync liveness failure where an outbound GetBlocks error could leave the orchestrator permanently stuck with in_flight = true.

The P2P layer now tracks outbound block-range request IDs and emits the internal-only SyncEvent::RequestFailed event when one of those requests fails. GetHeight failures are deliberately excluded so they cannot clear an unrelated block request.

The sync orchestrator clears in_flight on that event, allowing a later height response or block-gap announcement to restart synchronization.

request_next_batch() now returns true only when the SyncCommand was successfully accepted by the command channel.

Regression tests cover:

• forwarding a GetBlocks outbound failure;
• not forwarding a GetHeight failure as a block-request failure;
• retrying after the orchestrator receives RequestFailed;
• leaving in_flight false when the command receiver has been dropped.

No locked surfaces affected. This changes only in-process request tracking and node orchestration. SyncRequest, SyncResponse, SyncNotification, SCALE encodings, protocol strings, MAX_RANGE, consensus, storage semantics, and RPC contracts are unchanged.

Linked Issue

Closes #146

Scope Confirmation

• Targets dev branch
• Linked to an open issue
• Does not modify consensus logic unless explicitly scoped
• Does not introduce new cryptographic primitives unless explicitly scoped

Determinism Checklist

• Deterministic replay verified
• No state transition divergence
• Replay harness passes

Security Checklist

• I understand all code submitted
• Reviewed overflow / underflow risks
• Reviewed error handling paths
• Added unit tests if applicable

Testing

cargo +1.94.0 fmt --all -- --check
PASS

cargo +1.94.0 clippy --all-targets --all-features -- -D warnings
PASS

cargo test --workspace
PASS

cargo run -p mbongo-node --bin replay_harness
DETERMINISTIC REPLAY: PASS

cargo run -p mbongo-node --bin devnet_harness
DEVNET CONVERGENCE: PASS

git diff --check
PASS