Fix type of LabelClasses.classes

[lossyrob]

Currently setting a LabelClasses.classes property to List[str] gives an error in Pylance, e.g.

classes: List[str] = ...
label = LabelExtension.ext(item, add_if_missing=True)
label.apply(
    label_description="USGS GAP/LANDFIRE",
    label_type=LabelType.RASTER,
    label_classes=[
        LabelClasses.create(
            classes=classes,
            name="",
        )
    ],
)

yields error at classes=classes with

Argument of type "list[str]" cannot be assigned to parameter "classes" of type "List[str | int | float]" in function "create"
  TypeVar "_T@list" is invariant
    Type "str" cannot be assigned to type "str | int | float"
      "str" is incompatible with "int"
      "str" is incompatible with "float"

This I believe is due to the Union type as the generic to List here and here

This should be Union[List[str], List[int], List[float]] instead.

Bonus: search for other instances of List[Union[...]] and convert to Union[List[.], List[.], ...] to avoid a similar issue if it exists elsewhere.

[cuttlefish]

Is there a reason to use List over Sequence here? It probably doesn't make sense to take mutable data types as inputs?
I believe that Sequence can maintain the heterogeneity of the datatype (which may not be desired in this specific case, but would be useful elsewhere).
I've got a branch with the Label extension converted to use Sequence if there's any interest. This would probably only make sense if we were intending to transition everything over to Sequence.

[duckontheweb]

Closed via #627