sch.components.get() returns only the first unit instance for a given
reference. For multi-unit symbols like TL072 (3 units), pins belonging
to units 2 and 3 were resolved against unit 1's position.
Added pin-to-unit mapping via KiCad sub-symbol naming convention
(e.g. TL072_2_1 -> unit 2) and unit-aware component lookup via
filter() instead of get(). Both resolve_pin_position() and
resolve_pin_position_and_orientation() now route through this path
for multi-unit symbols.
