Move MQTT debug_info to dataclass

[jbouwh]

Proposed change

Move MQTT debug_info to dataclass

This is a follow-up PR on #77972

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[probot-home-assistant]

Hey there @emontnemery, mind taking a look at this pull request as it has been labeled with an integration (mqtt) you are listed as a code owner for? Thanks!
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[jbouwh]

Comments were followed up. #78706 is another PR in this collection.

[epenet]

A couple of comments:

• there are a couple of functions where type hints were only partially added
• with get_mqtt_data a few variables are unnecessary and the code can be put in a single line

[epenet]

Just two more that we have missed

[epenet]

LGTM
Maybe @cdce8p has some comments before merge?

[jbouwh]

Merging this now, so I can go in with #78706. any late reviews are still welcome.