Barrel contacts for vias/THT pads; configurable cap-drill threshold

- Selected vias and through-hole pads inject at the drill-wall ring on
  every spanned layer (both contact models), not the whole pad face,
  so the pad/pour spreading resistance is part of the result. Vias are
  now selectable as contacts.
- Soldered THT joints: the hole is modeled solder-filled (core in
  parallel with the plating, also for stitching THT barrels) and the
  pad face carries an average-thickness solder coat over the modeled
  copper (SOLDER_THICKNESS_UM).
- Vias with drills above a configurable threshold (dialog field,
  default CAP_MAX_DRILL_MM = 0.5) keep open mouths even with capping
  selected - the fab caps only small vias.
- Geometry dump schema v6: electrode barrel fields, cap_max_drill_nm.
- Verified against R = rho/(pi t)*acosh(d/2a) for two circular contacts
  on a sheet (+2.6% at h = 0.15 mm, a = 1 mm; uniform model above the
  equipotential one as required by the contact bracket).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

fill_resistance/standalone.py

@@ -42,6 +42,10 @@ def main(argv=None) -> int:
     ap.add_argument("--uncapped", action="store_true",
                     help="treat vias as uncapped (open drill mouths on "
                          "all layers)")
+    ap.add_argument("--cap-max-drill", type=float, default=None,
+                    metavar="MM",
+                    help="cap only vias with drill <= this [mm]; larger "
+                         "drills stay open (default: from the dump)")
     ap.add_argument("--extra-cu-um", type=float, default=None,
                     help="override the added copper in mask openings [um]")
     ap.add_argument("--force-iterative", action="store_true",
@@ -68,6 +72,8 @@ def main(argv=None) -> int:
         problem.buildups = []
     if args.uncapped:
         problem.vias_capped = False
+    if args.cap_max_drill is not None:
+        problem.cap_max_drill_nm = int(args.cap_max_drill * 1e6)
     if args.extra_cu_um is not None:
         problem.extra_cu_nm = int(args.extra_cu_um * 1000)
     if args.layers: