Route wider net classes at their width, falling back where they don't fit

The grid is laid out for the default width; a wider trace also needs the
cells its extra half width reaches to be free, and claims a wider halo.
A connection that does not fit at its class width (typically at a
fine-pitch pin) is routed at the default instead and reported. A net is
written at its class width when all of its connections went in at it,
and the exact check verifies it at that width; nets that shove or the
diagonal pass reshaped go out at the default.

src/freeroute/cli.py

@@ -287,6 +287,14 @@ def main(argv: list[str] | None = None) -> int:
         print(f"freeroute: {len(missing)} connection(s) not routed:", file=sys.stderr)
         for net, a, b, _zone in missing:
             print(f"  {net}: {a} to {b}", file=sys.stderr)
+    if result.narrowed:
+        print(
+            f"freeroute: {len(result.narrowed)} connection(s) of a wider net class only fitted "
+            "at the default width; their nets are written at the default width:",
+            file=sys.stderr,
+        )
+        for net, a, b in result.narrowed:
+            print(f"  {net}: {a} to {b}", file=sys.stderr)
     if in_zone:
         print(
             f"freeroute: {len(in_zone)} more connection(s) left to a zone fill that may join them:",