micropython/umqtt.simple/umqtt: Add support for to umqtt.simple.

[FallenPhoenix8]

Summary

1. Explicit UTF-8 Encoding:

• Both the topic and msg are now explicitly encoded using UTF-8 (topic.encode('utf-8') and msg.encode('utf-8')).

2. Accurate Size Calculation:

• The size of the message (sz) is calculated based on the byte length of the encoded topic and message.

[dpgeorge]

Thanks for the contribution, but I'm not sure exactly what this PR is fixing/improving.

The idea with the publish() method is that you should pass in bytes objects for topic and message. This PR will break existing uses of publish() that do pass in bytes (or bytearray) objects.

[FallenPhoenix8]

Ok, thanks for the information. I'll close the Pull Request.