Mux checks

[daniel-montanari]

Remove requirement to have both pin_list and pin_map which had issues in the new switching module if pins were missing from the list.

Add check that pins are unique across muxes.

[daniel-montanari]

Test is failing due to using the calculated pins, rather than the supplied pin_list

def test_jig_driver_with_unknown_pins():
    handler1 = AddressHandler(("x0",))
    handler2 = AddressHandler(("x2",))
    handler3 = AddressHandler(("x1",))

    class Mux(VirtualMux):
        pin_list = ("x0", "x1")  # "x1" isn't in either handler
        map_list = ("sig1", "x1")

    class Group(MuxGroup):
        def __init__(self):
            self.mux = Mux()

    # This is O.K., because all the pins are included
    JigDriver(Group, [handler1, handler2, handler3]) 
    # ^ test is failing here due to VirtualMux._validate, since self._pin_set is incorrect

    with pytest.raises(ValueError):
        # This should raise, because no handler implements "x1"
        JigDriver(Group, [handler1, handler2])

expected output for mux pins
{'sig1': frozenset({'x1'})}
actual output
{'s': frozenset({'1', 'g', 'i'}), 'x': frozenset({'1'})}

After switching back to main it looks like this test passes, but never produced a useable mux.

There isn't a great way to type this. Maybe we should enforce Sequence[tuple[str,...]]
str is a sequence, so str and Sequence[str] end up being the same thing in the eyes of mypy.