Defer esphome persistent storage writes until after startup

[bdraco]

Noticed because I have 35+ esphome devices.

Proposed change

Defer esphome persistent storage writes until after startup

Avoid disk I/O during startup as it can cause delays when
a user has many esphome devices.

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[probot-home-assistant]

Hey there @OttoWinter, mind taking a look at this pull request as its been labeled with an integration (esphome) you are listed as a codeowner for? Thanks!
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[balloob]

Nice one.

We should find all the async_save and make them delays unless it's auth related (user/config entry).

[bdraco]

I'll audit what else is done at startup and adjust since these are the ones we except to be I/O bound since they are competing with loading the .py files from disk.

[balloob]

Is this going to be okay? If there never will be 2 minutes of no data, it will never save until HA is shut down.

[bdraco]

Should be fine since it only needs the data to re-setup the config entries with the last state before its able to make the connection to the device.

[balloob]

For other use cases, we could consider adding a max_wait to delay_save to make sure it's written eventually (besides on shutdown).