Fix device info timeout in TOU schedule example

[eman]

Problem

The tou_schedule_example.py was consistently timing out when trying to get the controller serial number, showing this error:

Requesting controller serial number via device info...
Timed out waiting for device features

Root Cause

The _wait_for_controller_serial function was using the event emitter to wait for feature_received events without first subscribing to device feature messages:

# ❌ Problematic code
mqtt_client.once("feature_received", capture_feature)
await mqtt_client.request_device_info(device)

The feature_received event is only emitted when a device feature message is received and parsed by a subscribed handler. Without the subscription, the MQTT client never receives the response messages.

Solution

Fixed the function to properly subscribe to device feature messages before making the request:

# ✅ Fixed code
await mqtt_client.subscribe_device_feature(device, capture_feature)
await mqtt_client.request_device_info(device)

This ensures:

1. MQTT subscription is established for device feature messages
2. The response messages are received and parsed
3. The feature_received event is properly emitted
4. The timeout is avoided

Verification

• Pattern now matches successful examples like device_feature_callback.py
• Other event emitter usage (like event_emitter_demo.py) is correctly implemented
• Code passes linting and formatting checks

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature
• Breaking change
• Documentation update

Impact

This fix ensures the TOU schedule example works correctly and can successfully retrieve the controller serial number needed for TOU operations.