Allow representing paths as pathlib.Path

[bkeryan]

Problem to Solve

Python 3.x has a standard data type for paths, pathlib.Path, but we are not using it. Specifying that has a configuration parameter has a data type of ni_measurementlink_service.DataType.Path yields a str, not a pathlib.Path.

Proposed Solution

Interpret ni_measurementlink_service.DataType.Path as pathlib.Path, possibly with a opt-in for compatibility.

AB#2414585

[bkeryan]

How does this work for enums?

@measurement_service.configuration(
    "measurement_type", nims.DataType.Enum, Function.DC_VOLTS, enum_type=Function
)

enum_type is used to build the annotations dictionary, but it's not actually used to construct enum values: https://github.com/ni/measurementlink-python/blob/main/ni_measurementlink_service/measurement/service.py#L309

Instead, we use type(parameter_metadata.default_value) to get the enum type: https://github.com/ni/measurementlink-python/blob/main/ni_measurementlink_service/_internal/parameter/serializer.py#L249

We could use the same approach to get the path type:

# use str
@measurement_service.configuration("levels_file_path", nims.DataType.Path, "PinLevels.digilevels")

# use pathlib.Path
@measurement_service.configuration("levels_file_path", nims.DataType.Path, pathlib.Path("PinLevels.digilevels"))

[bkeryan]

This approach would not work for path arrays when the default value is an empty list, because there is no 1st element from which to infer the element type. See #366