Merge pull request 'Improved placement of power rail vias' (#21) from Sourcerer/lclayout:main into main

Reviewed-on: https://codeberg.org/librecell/lclayout/pulls/21

* instead introduce the `magscale` parameter for `MagicWriter`
* use `magscale` parameter in the tech-file to set the correct scale

This reverts commit f84b5b28.

This reverts commit 60392378.

Dict

This should be changed into an additional magscale parameter in the
.tech file instead

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.