Hole spacing to a fixed via measured from where it is, with its own drill

A fixed via sits anywhere, not on a cell centre, and may have a bigger
drill than the router's via; checking hole spacing between cell centres
with one drill let the flight controller's routed 0.2 mm via come 0.19
mm from a hand-placed 0.25 mm one. The board now carries each fixed
via's drill (from KiCad's padstack name), and cells are checked against
fixed vias exactly.

src/freeroute/board/build.py

@@ -23,6 +23,7 @@ the containment invariant, and pads are centre-symmetric in practice).
 from __future__ import annotations
 
 import math
+import re
 
 from freeroute.dsn.model import DsnBoard
 from freeroute.dsn.shapes import Circle, Path, Polygon, Rectangle, Shape
@@ -38,6 +39,9 @@ from .transform import CoordinateTransform
 
 __all__ = ["build_board"]
 
+# DSN units per micrometre, for drills KiCad gives in um in via padstack names
+_DSN_PER_UM = {"um": 1.0, "mm": 0.001, "mil": 1 / 25.4, "inch": 1 / 25400}
+
 
 def build_board(dsn: DsnBoard) -> BasicBoard:
     """Construct a :class:`BasicBoard` from a parsed :class:`DsnBoard`."""
@@ -503,10 +507,15 @@ def _insert_wiring(dsn: DsnBoard, board: BasicBoard, transform: CoordinateTransf
         location = transform.dsn_to_board_point(via.x, via.y)
         pad = _pad_tile(max(padstack.shapes, key=_shape_extent), transform)
         box = pad.bounding_box()
+        drill = re.search(r"_([\d.]+):([\d.]+)_um", via.padstack)
+        drill_board = (
+            round(transform.dsn_to_board(float(drill.group(2)) * _DSN_PER_UM.get(dsn.unit, 1.0)))
+            if drill else 0
+        )
         board.insert(
             Via(
                 net_nos=[numbers[via.net]], fixed=True, padstack_name=via.padstack,
-                location=location, layers=sorted(layers or signal_layers),
+                drill=drill_board, location=location, layers=sorted(layers or signal_layers),
                 shape=IntBox(box.ll.x + location.x, box.ll.y + location.y,
                              box.ur.x + location.x, box.ur.y + location.y),
             )