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/ses/model.py

@@ -60,6 +60,9 @@ class RoutingResult:
     #: connections the router could not make: (net name, one end, other end,
     #: the zone both ends sit in or "") -- a zone's fill may join the latter
     unrouted: list[tuple[str, str, str, str]] = field(default_factory=list)
+    #: connections of a wider net class that only fitted at the default width
+    #: (net name, one end, other end); their net is written at the default
+    narrowed: list[tuple[str, str, str]] = field(default_factory=list)
 
     def net(self, name: str, *, create: bool = False) -> RoutedNet | None:
         """Return the :class:`RoutedNet` with ``name`` (creating it if asked)."""