fix(platform/messaging): receive latest retained message per topic in…

… wildcard subscription

Previously, a wildcard subscription received only the latest retained message that matched the subscription, even if the messages were published to different topics. Now the subscription receives the latest retained message per matching topic.

### Example
Imagine having the following retained messages and subscribing to 'myhome/:room/temperature'.
- 'myhome/livingroom/temperature': 22°C (message 1)
- 'myhome/kitchen/temperature': 21°C (message 2)
- 'myhome/kitchen/temperature': 21.5°C (message 3)
- 'myhome/diningroom/temperature': 20.5°C (message 4)

The subscription now receives the following messages:
- 'myhome/livingroom/temperature': 22°C (message 1)
- 'myhome/kitchen/temperature': 21.5°C (message 3)
- 'myhome/diningroom/temperature': 20.5°C (message 4)

Previously, only the following message was received:
- 'myhome/diningroom/temperature': 20.5°C (message 4)