Use `interacts` instead of `is_inside`. If the via shape is closer than
`margin` to shapes on the `other_layer`, then the via location is
invalid. `interacts` checks if a point is closer than `margin` to a set
of polygons `region`.
`is_inside` checks if a point is inside the `region` while having a
distance to the polygon edges of at least `margin`.

Due to "interact" instead of "is_inside" vias had to spaced further away
than the DRC rules specify

* By default, use the gate lengths defined in the SPICE netlist.
* Can overwrite the gate lengths in the tech file using
  `gate_length_nmos` and `gate_length_pmos` variables.