Add more type ignore to the FormulaEngine

The code already had a bunch of `type: ignore[type-arg]` because some
generic types are missing the type argument. For some reason it seems
like previous `mypy` versions didn't complain about this for all cases,
but now it does.

Signed-off-by: Leandro Lucarella <[email protected]>

Author: llucax

src/frequenz/sdk/timeseries/formula_engine/_formula_engine.py

@@ -54,34 +54,36 @@
 }
 """The dictionary of operator precedence for the shunting yard algorithm."""
 
+
+# The `FormulaEngine*` and `HigherOrderFormulaBuilder*` classes are generic, but
+# `TypeVar`s can't be defined on generic types, so we need to use `# type: ignore` to
+# avoid mypy errors, and they get treated as `FormulaEngine[Any]`, etc.
+#
+# This is not ideal, but it's the best we can do until mypy supports generic types with
+# `TypeVar`s.
 _CompositionType = Union[
-    "FormulaEngine",
-    "HigherOrderFormulaBuilder",
-    "FormulaEngine3Phase",
-    "HigherOrderFormulaBuilder3Phase",
+    "FormulaEngine",  # type: ignore[type-arg]
+    "HigherOrderFormulaBuilder",  # type: ignore[type-arg]
+    "FormulaEngine3Phase",  # type: ignore[type-arg]
+    "HigherOrderFormulaBuilder3Phase",  # type: ignore[type-arg]
 ]
 
 _CompositionType1Phase = Union[
-    "FormulaEngine",
-    "HigherOrderFormulaBuilder",
+    "FormulaEngine",  # type: ignore[type-arg]
+    "HigherOrderFormulaBuilder",  # type: ignore[type-arg]
 ]
 
 _CompositionType3Phase = Union[
-    "FormulaEngine3Phase",
-    "HigherOrderFormulaBuilder3Phase",
+    "FormulaEngine3Phase",  # type: ignore[type-arg]
+    "HigherOrderFormulaBuilder3Phase",  # type: ignore[type-arg]
 ]
 
-# The `FormulaEngine*` and `HigherOrderFormulaBuilder*` classes are generic, but
-# `TypeVar`s can't be defined on generic types, so we need to use `# type: ignore` to
-# avoid mypy errors, and they get treated as `FormulaEngine[Any]`, etc.
-#
-# This is not ideal, but it's the best we can do until mypy supports generic types with
-# `TypeVar`s.
 _GenericEngine = TypeVar(
     "_GenericEngine",
     "FormulaEngine",  # type: ignore
     "FormulaEngine3Phase",  # type: ignore
 )
+
 _GenericHigherOrderBuilder = TypeVar(
     "_GenericHigherOrderBuilder",
     "HigherOrderFormulaBuilder",  # type: ignore