Typing: fix MessageData annotations and modernize (TypedDict/slots)

[ff225]

Priority: Medium

Typing correctness and modernization.

Tasks

• Fix MessageData dataclass annotations, which are wrong: payload: str is actually bytes; device_id: int is a str; message_id: int is a str; message_content: str is a dict; timestamp: str is a float. Dynamically-added attributes (received_timestamp, avg_speed, …) are class variables defaulting to None instead of real dataclass fields.
• Adopt TypedDict for recurring config structures and dataclass(slots=True) where beneficial (project requires Python ≥3.12).

Files

• src/server/communication/message_data.py
• recurring config structures

From the Feature 042 codebase review (recommendations #5, #15).