Cache the response from config/entity_registry/list

[bdraco]

This is part of an optimization cycle to improve the responsiveness of the UI during first pickup and startup

Proposed change

Reverts #74378 and replaces this with a cache instead.

When doing additional testing, the list comp was still
slow on my RPI 32bit test platform, and we still had
the json encode overhead (while its much better with
orjson, its still not trivial).

This reduces the CPU spike
when everything reconnects at startup. The device
registry does show up on the profile still, and while its
small for one device reconnecting, it could have an impact
if they have 5-6 and the system is cpu bound during startup
so we might want to do that one as well in the future
but addressing the static files path is probably time
better spent.

Flame graph of an initial websocket connect
on cache hit its below the sampling threshold.

And yes it does look like static files call pathlib which is doing
I/O in the event loop but that seems to be copied from
aiohttp so I'm not sure if it should or not

Similar strategy as

core/homeassistant/components/websocket_api/messages.py

Line 70 in ebc8fba

def cached_event_message(iden: int, event: Event) -> str:

except its cleared when the registry is updated instead of the
event itself

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[bdraco]

We should probably resolve the symlink and stat the files in the executor. It might make the request a bit slower though. The upside is that if you open the UI during startup when the system is IO bound it won't block the event loop waiting to be able to run the readlink/stat syscslls

[bdraco]

Actually for the frontend files if we aren't in dev mode it might make more sense to cache the filepath lookup

[bdraco]

This one should be good to go. #74474 takes care of the existing I/O in the event loop