Simplify emulated_hue exposed entities cache

[bdraco]

Proposed change

Also avoids holding stale States in memory which can prevent garbage collection of linked contexts

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[home-assistant]

Hey there @Tho85, mind taking a look at this pull request as it has been labeled with an integration (emulated_hue) you are listed as a code owner for? Thanks!

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[balloob]

We're caching something here that relies on he state machine. I know that's existing code but that seems weird ?

[bdraco]

The cache gets cleared in the function below it when needed. We watch when new states are being added and removed to/from the state machine in async_setup and clear the cache when they are.

[bdraco]

We only use the cache to figure out what is exposed. The state machine still gets polled every api request unfortunately

def create_list_of_entities(config: Config, request: web.Request) -> dict[str, Any]:
    """Create a list of all entities."""
    hass: core.HomeAssistant = request.app["hass"]
    return {
        config.entity_id_to_number(entity_id): state_to_json(config, state)
        for entity_id in config.get_exposed_entity_ids()
        if (state := hass.states.get(entity_id))
    }

That could watch states and only do state_to_json when they actually change.. but thats something for the future, and now I'm a bit off topic