Make FormulaEngines generic over Quantity types

This commit also updates the generated formulas to use the right
generic types like Power and Current, for power and current formulas
respectively.

Signed-off-by: Sahas Subramanian <[email protected]>

Author: shsms

examples/power_distribution.py

@@ -22,7 +22,7 @@
 from frequenz.sdk.actor import ResamplerConfig
 from frequenz.sdk.actor.power_distributing import Result, Success
 from frequenz.sdk.timeseries import Sample
-from frequenz.sdk.timeseries._quantities import Quantity
+from frequenz.sdk.timeseries._quantities import Power
 
 _logger = logging.getLogger(__name__)
 HOST = "microgrid.sandbox.api.frequenz.io"  # it should be the host name.
@@ -98,7 +98,7 @@ class DataCollectingActor:
     def __init__(
         self,
         request_channel: Sender[List[float]],
-        active_power_data: Receiver[Sample[Quantity]],
+        active_power_data: Receiver[Sample[Power]],
     ) -> None:
         """Create actor instance.