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/server/eosdash.py

@@ -110,13 +110,13 @@ def main() -> None:
     parser.add_argument(
         "--host",
         type=str,
-        default=str(config_eos.server_eosdash_host),
+        default=str(config_eos.server.server_eosdash_host),
         help="Host for the EOSdash server (default: value from config_eos)",
     )
     parser.add_argument(
         "--port",
         type=int,
-        default=config_eos.server_eosdash_port,
+        default=config_eos.server.server_eosdash_port,
         help="Port for the EOSdash server (default: value from config_eos)",
     )
 
@@ -124,13 +124,13 @@ def main() -> None:
     parser.add_argument(
         "--eos-host",
         type=str,
-        default=str(config_eos.server_eos_host),
+        default=str(config_eos.server.server_eos_host),
         help="Host for the EOS server (default: value from config_eos)",
     )
     parser.add_argument(
         "--eos-port",
         type=int,
-        default=config_eos.server_eos_port,
+        default=config_eos.server.server_eos_port,
         help="Port for the EOS server (default: value from config_eos)",
     )