P2-20 FirmwareEngine batch serial output messages (realtime)

[Kinin-Code-Offical]

(Synced from docs/current_status/issue_ready_backlog.md)\n\n# P2-20 FirmwareEngine batch serial output messages (realtime)\n\nSummary

• Area: FirmwareEngine
• Deliverable: coalesce serial bytes per tick/message.

Acceptance Criteria

• Serial output frames can carry multiple bytes (or are batched per tick).
• Clients handle batched data correctly.

Test Plan

• Integration: run sketch that prints frequently; verify throughput and correctness.

Likely File Targets

• FirmwareEngine protocol + serial output handling
• Clients: CoreSim/Unity serial parsing

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