Fix EchoReader blocking indefinitely after transient exceptions

[Copilot]

After any exception in the reader loop (e.g., serial/UDP drop), run_forever fell through to await self._restart_event.wait() — blocking until settings were manually updated, with no automatic recovery.

Changes

• Retry with exponential backoff on exceptions: on error, sleeps 1s → 2s → 4s → … → 30s cap, then retries automatically
• _restart_event.wait() only on clean exit: moved inside the try block so exceptions take the backoff path instead
• Backoff resets on clean exit: after a deliberate settings-driven restart, the delay counter resets to 1s

# Before: exceptions always fell through to this, blocking forever
await self._restart_event.wait()

# After: clean exit waits for restart; exceptions retry with backoff
try:
    async with reader:
        async for pkt in reader:
            ...
    retry_delay = 1  # reset on clean exit
    await self._restart_event.wait()
except Exception as e:
    log.error(f"❌ Error in EchoReader: {e}", exc_info=e)
    await asyncio.sleep(retry_delay)
    retry_delay = min(retry_delay * 2, 30)

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