Avoid importing MQTT into core for ServiceInfo dataclass

[bdraco]

Proposed change

Which ever integration triggered the first discovery flow would trigger the python code for mqtt to be loaded. Since most flows would wait until after startup since we queue them until the started event if they come from discovery, this meant that the rpi_power integration which is triggered from the raspberry_pi hardware integration would cause this to happen a lot sooner on RPI platforms. MQTT python code loading would happen at an unexpected time which is a blocking operation since the python files have to be loaded from disk. This caused warnings since everything was waiting for MQTT code load (which takes 8s on my x86_64 spinning disk machine and likely longer on RPi3b+s with an sd card)

Likely fixes #73863

A nice side effect is that if you aren't using MQTT, this saves ~20MiB of RAM on 64bit platforms

I will move the rest of them in a followup PR but I didn't want to do that now since this one should go into beta since they will already be loaded anyways if they are enabled and don't have this issue, but its better to be consistant and have them all in one place in case we add more in the future.

MQTT was getting loaded via config flow since it was needed to type async_step_mqtt

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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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[probot-home-assistant]

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

Its still going to hit __init__.py

[bdraco]

This still takes 8s on my spinning disk system

>>> from homeassistant.components.mqtt.service_info import MqttServiceInfo

[bdraco]

I think we need to relo all these dataclasses into their own area

[bdraco]

Was on the fence on if this was worth the churn but after #75183 I'm not on the fence anymore and will move this foward and do followups for bluetooth, and the others.