Add TileShape and Simplex convex-shape core

Ports geometry/planar/TileShape.java (the border-line-based containment,
area, and centre-of-gravity logic) and Simplex.java (a convex region as
the intersection of directed half-planes). Corners are exact
intersections of consecutive border lines; point containment uses exact
side_of. The remove_redundant_lines normalization — dropping lines that
do not contribute and detecting emptiness — is ported line-for-line.

Supporting additions: Line.compare_to/__lt__ (angular sort order),
Line.fast_equals, Line.side_of_intersection, Line.translate (perpendicular
offset), IntDirection.determinant, and IntBox.to_simplex.

offset is approximate (rounded translated lines, as upstream); enlarge
clips to the enlarged bounding box pending the IntOctagon port.

Since there is no JVM oracle, tests assert invariants: corners lie
exactly on their border lines (exact side_of == 0), IntBox -> Simplex
preserves the region over a sampled grid, intersection is contained in
both operands and a point is in the result iff in both, and get_instance
normalization drops redundant lines and detects empty half-plane pairs.

src/freeroute/geometry/direction.py

@@ -109,6 +109,10 @@ class IntDirection(Direction):
         nx, ny = table[n]
         return IntDirection(nx, ny)
 
+    def determinant(self, other: IntDirection) -> int:
+        """Exact determinant of the two direction vectors."""
+        return self.x * other.y - self.y * other.x
+
     def compare_to(self, other: Direction) -> int:
         """Angular comparison with the positive x-axis (exact).