Mypy (#217)

* Mypy: Initial support

 * Add to pre-commit (currently installs own deps, could maybe changed
   to poetry venv in the future to reuse environment and don't need
   duplicated types deps).
 * Add type hints.

* Mypy: Add missing annotations

src/akkudoktoreos/devices/inverter.py

@@ -4,7 +4,7 @@ from akkudoktoreos.devices.battery import PVAkku
 
 
 class WechselrichterParameters(BaseModel):
-    max_leistung_wh: float = Field(10000, gt=0)
+    max_leistung_wh: float = Field(default=10000, gt=0)
 
 
 class Wechselrichter:
@@ -14,9 +14,11 @@ class Wechselrichter:
         )
         self.akku = akku  # Connection to a battery object
 
-    def energie_verarbeiten(self, erzeugung, verbrauch, hour):
-        verluste = 0  # Losses during processing
-        netzeinspeisung = 0  # Grid feed-in
+    def energie_verarbeiten(
+        self, erzeugung: float, verbrauch: float, hour: int
+    ) -> tuple[float, float, float, float]:
+        verluste = 0.0  # Losses during processing
+        netzeinspeisung = 0.0  # Grid feed-in
         netzbezug = 0.0  # Grid draw
         eigenverbrauch = 0.0  # Self-consumption