Parts Table Refactor

[ducky64]

Cleans up the parts table type hierarchy, with more orthogonality between the part, abstract-table, footprint-spec, footprint-area, and footprint-generation functionality.

Other changes:

• Adds ClassVar[...] to some abstract class variables that are to be implemented by subclasses, but it seems mypy won't detect those without ABCmeta, which breaks a bunch of other stuff. Sad.
• Moves the standard-footprint functionality to its own class, and the HasStandardFootprint interface. HasStandardFootprint now implemented by abstract classes like Bjt, Capacitor, ..., instead of the more specific table. Also includes the refdes prefix.
• Uniformly support footprint-spec and footprint-area filters on the base JlcTable class. The footprint generation must be mixed into each subclass independently, since some devices do not support standard footprints (antenna) or generate sub-blocks (oscillator)
• Makes the PartsTablePart (and hierarchy) abstract library parts (instead of non-library) and browseable.
• Adds *args, **kwargs forwarding in base FootprintBlock and GeneratorBlock classes.