Store runtime data inside the config entry

Integrations often need to set up and track custom data, such as coordinators, API connections, or code objects. Previously, those were all stored inside hass.data, which made tracking them difficult.

With recent changes, it's now possible to use entry.runtime_data for that. The config entry is already available when setting up platforms and gets cleaned up automatically. No more deleting the key from hass.data after unloading.

It also better supports type-checking. ConfigEntry is generic now, so passing the data type along is possible. Use a typed data structure like dataclass for that. To simplify the annotation, it's recommended to define a type alias for it.

An example could look like this:

# <integration>/__init__.py

# The type alias needs to be suffixed with 'ConfigEntry'
type MyConfigEntry = ConfigEntry[MyData]

@dataclass
class MyData:
    client: MyClient
    other_data: dict[str, Any]

async def async_setup_entry(
    hass: HomeAssistant,
    entry: MyConfigEntry,  # use type alias instead of ConfigEntry
) -> bool:
    client = MyClient(...)
    
    # Assign the runtime_data
    entry.runtime_data = MyData(client, {...})

# <integration>/switch.py

from . import MyConfigEntry

async def async_setup_entry(
    hass: HomeAssistant,
    entry: MyConfigEntry,  # use type alias instead of ConfigEntry
    async_add_entities: AddEntitiesCallback,
) -> None:
    # Access the runtime data form the config entry
    data = entry.runtime_data
    
    async_add_entities([MySwitch(data.client)])