fix: energy charts bidding zone in request (#948)

Ensure that the bidding zone in the request is correctly set to a
string value (not an enum).

This seems to be also an issue with python version < 3.11. Add safeguards
to only use python >= 3.11. Still keep a regression test for the enum
conversion to string.

Signed-off-by: Bobby Noelte <b0661n0e17e@gmail.com>

src/akkudoktoreos/core/emsettings.py

@@ -3,38 +3,20 @@
 Kept in an extra module to avoid cyclic dependencies on package import.
 """
 
-from enum import Enum
-from typing import Optional, Union
+from enum import StrEnum
 
 from pydantic import Field
 
 from akkudoktoreos.config.configabc import SettingsBaseModel, is_home_assistant_addon
 
 
-class EnergyManagementMode(str, Enum):
+class EnergyManagementMode(StrEnum):
     """Energy management mode."""
 
     DISABLED = "DISABLED"
     PREDICTION = "PREDICTION"
     OPTIMIZATION = "OPTIMIZATION"
 
-    @classmethod
-    def is_valid(cls, mode: Union[str, "EnergyManagementMode"]) -> bool:
-        """Check if value is a valid mode."""
-        try:
-            cls(mode)
-            return True
-        except (ValueError, TypeError):
-            return False
-
-    @classmethod
-    def from_value(cls, value: str) -> Optional["EnergyManagementMode"]:
-        """Safely convert string to enum, return None if invalid."""
-        try:
-            return cls(value)
-        except ValueError:
-            return None
-
 
 def ems_default_mode() -> EnergyManagementMode:
     """Provide default EMS mode.