Support for pull-based advert requests and responses.

[michielappelman]

Adds support for requesting extended advertisement data from nodes on demand. As described in meshcore-dev/MeshCore#1374

Changes

• commands.py: Added request_advert(prefix, path) command (CMD 0x39)
• reader.py: Added parser for PUSH_CODE_ADVERT_RESPONSE (0x8F)
• events.py: Added ADVERT_RESPONSE event type

Usage

# Request advert from node with prefix 0x1F
result = await mc.commands.request_advert(bytes([0x1F]), bytes([0x1F]))

# Wait for async response
response = await mc.wait_for_event(EventType.ADVERT_RESPONSE, timeout=30)
if response:
    print(f"Name: {response.payload['node_name']}")
    print(f"Location: {response.payload.get('latitude')}, {response.payload.get('longitude')}")
    print(f"Description: {response.payload.get('node_desc')}")