Nested config, devices registry

* All config now nested.
    - Use default config from model field default values. If providers
      should be enabled by default, non-empty default config file could
      be provided again.
    - Environment variable support with EOS_ prefix and __ between levels,
      e.g. EOS_SERVER__EOS_SERVER_PORT=8503 where all values are case
      insensitive.
      For more information see:
      https://docs.pydantic.dev/latest/concepts/pydantic_settings/#parsing-environment-variable-values
    - Use devices as registry for configured devices. DeviceBase as base
      class with for now just initializion support (in the future expand
      to operations during optimization).
    - Strip down ConfigEOS to the only configuration instance. Reload
      from file or reset to defaults is possible.

 * Fix multi-initialization of derived SingletonMixin classes.

src/akkudoktoreos/prediction/prediction.py

@@ -80,13 +80,13 @@ class PredictionCommonSettings(SettingsBaseModel):
         description="Number of hours into the past for historical predictions data",
     )
     latitude: Optional[float] = Field(
-        default=None,
+        default=52.52,
         ge=-90.0,
         le=90.0,
         description="Latitude in decimal degrees, between -90 and 90, north is positive (ISO 19115) (°)",
     )
     longitude: Optional[float] = Field(
-        default=None,
+        default=13.405,
         ge=-180.0,
         le=180.0,
         description="Longitude in decimal degrees, within -180 to 180 (°)",