refactor: pass B2Segment as readonly in and update callers

Change segment collision helpers to take B2Segment by 'in' instead of 'ref'.
Update contacts, shape setter, and sample call sites accordingly.
This better reflects readonly intent and avoids unnecessary ref usage.

Author: ikpil

src/Box2D.NET.Samples/Samples/Collisions/Manifold.cs

@@ -283,7 +283,7 @@ public override void Step()
             B2Transform transform1 = new B2Transform(offset, b2Rot_identity);
             B2Transform transform2 = new B2Transform(b2Add(m_transform.p, offset), m_transform.q);
 
-            B2Manifold m = b2CollideSegmentAndCircle(ref segment, transform1, ref circle, transform2);
+            B2Manifold m = b2CollideSegmentAndCircle(segment, transform1, ref circle, transform2);
 
             B2Vec2 p1 = b2TransformPoint(transform1, segment.point1);
             B2Vec2 p2 = b2TransformPoint(transform1, segment.point2);
@@ -367,7 +367,7 @@ public override void Step()
             B2Transform transform1 = new B2Transform(offset, b2Rot_identity);
             B2Transform transform2 = new B2Transform(b2Add(m_transform.p, offset), m_transform.q);
 
-            B2Manifold m = b2CollideSegmentAndCapsule(ref segment, transform1, capsule, transform2);
+            B2Manifold m = b2CollideSegmentAndCapsule(segment, transform1, capsule, transform2);
 
             B2Vec2 p1 = b2TransformPoint(transform1, segment.point1);
             B2Vec2 p2 = b2TransformPoint(transform1, segment.point2);
@@ -473,7 +473,7 @@ public override void Step()
             B2Transform transform2 = new B2Transform(b2Add(m_transform.p, offset), m_transform.q);
             // b2Transform transform2 = {b2Add({-1.44583416f, 0.397352695f}, offset), m_transform.q};
 
-            B2Manifold m = b2CollideSegmentAndPolygon(ref segment, transform1, ref rox, transform2);
+            B2Manifold m = b2CollideSegmentAndPolygon(segment, transform1, ref rox, transform2);
 
             B2Vec2 p1 = b2TransformPoint(transform1, segment.point1);
             B2Vec2 p2 = b2TransformPoint(transform1, segment.point2);

src/Box2D.NET.Samples/Samples/Shapes/ModifyGeometry.cs

@@ -91,7 +91,7 @@ void UpdateShape()
 
             case B2ShapeType.b2_segmentShape:
                 m_us.segment = new B2Segment(new B2Vec2(-0.5f * m_scale, 0.0f), new B2Vec2(0.75f * m_scale, 0.0f));
-                b2Shape_SetSegment(m_shapeId, ref m_us.segment);
+                b2Shape_SetSegment(m_shapeId, m_us.segment);
                 break;
 
             case B2ShapeType.b2_polygonShape:

src/Box2D.NET/B2Contacts.cs

@@ -81,19 +81,19 @@ internal static B2Manifold b2PolygonManifold(B2Shape shapeA, in B2Transform xfA,
         internal static B2Manifold b2SegmentAndCircleManifold(B2Shape shapeA, in B2Transform xfA, B2Shape shapeB, in B2Transform xfB, ref B2SimplexCache cache)
         {
             B2_UNUSED(cache);
-            return b2CollideSegmentAndCircle(ref shapeA.us.segment, xfA, ref shapeB.us.circle, xfB);
+            return b2CollideSegmentAndCircle(shapeA.us.segment, xfA, ref shapeB.us.circle, xfB);
         }
 
         internal static B2Manifold b2SegmentAndCapsuleManifold(B2Shape shapeA, in B2Transform xfA, B2Shape shapeB, in B2Transform xfB, ref B2SimplexCache cache)
         {
             B2_UNUSED(cache);
-            return b2CollideSegmentAndCapsule(ref shapeA.us.segment, xfA, shapeB.us.capsule, xfB);
+            return b2CollideSegmentAndCapsule(shapeA.us.segment, xfA, shapeB.us.capsule, xfB);
         }
 
         internal static B2Manifold b2SegmentAndPolygonManifold(B2Shape shapeA, in B2Transform xfA, B2Shape shapeB, in B2Transform xfB, ref B2SimplexCache cache)
         {
             B2_UNUSED(cache);
-            return b2CollideSegmentAndPolygon(ref shapeA.us.segment, xfA, ref shapeB.us.polygon, xfB);
+            return b2CollideSegmentAndPolygon(shapeA.us.segment, xfA, ref shapeB.us.polygon, xfB);
         }
 
         internal static B2Manifold b2ChainSegmentAndCircleManifold(B2Shape shapeA, in B2Transform xfA, B2Shape shapeB, in B2Transform xfB, ref B2SimplexCache cache)

src/Box2D.NET/B2Manifolds.cs

@@ -537,7 +537,7 @@ public static B2Manifold b2CollideCapsules(in B2Capsule capsuleA, in B2Transform
         }
 
         /// Compute the contact manifold between an segment and a capsule
-        public static B2Manifold b2CollideSegmentAndCapsule(ref B2Segment segmentA, in B2Transform xfA, in B2Capsule capsuleB, in B2Transform xfB)
+        public static B2Manifold b2CollideSegmentAndCapsule(in B2Segment segmentA, in B2Transform xfA, in B2Capsule capsuleB, in B2Transform xfB)
         {
             B2Capsule capsuleA = new B2Capsule(segmentA.point1, segmentA.point2, 0.0f);
             return b2CollideCapsules(capsuleA, xfA, capsuleB, xfB);
@@ -1088,14 +1088,14 @@ public static B2Manifold b2CollidePolygons(ref B2Polygon polygonA, in B2Transfor
         }
 
         /// Compute the contact manifold between an segment and a circle
-        public static B2Manifold b2CollideSegmentAndCircle(ref B2Segment segmentA, in B2Transform xfA, ref B2Circle circleB, in B2Transform xfB)
+        public static B2Manifold b2CollideSegmentAndCircle(in B2Segment segmentA, in B2Transform xfA, ref B2Circle circleB, in B2Transform xfB)
         {
             B2Capsule capsuleA = new B2Capsule(segmentA.point1, segmentA.point2, 0.0f);
             return b2CollideCapsuleAndCircle(capsuleA, xfA, ref circleB, xfB);
         }
 
         /// Compute the contact manifold between an segment and a polygon
-        public static B2Manifold b2CollideSegmentAndPolygon(ref B2Segment segmentA, in B2Transform xfA, ref B2Polygon polygonB, in B2Transform xfB)
+        public static B2Manifold b2CollideSegmentAndPolygon(in B2Segment segmentA, in B2Transform xfA, ref B2Polygon polygonB, in B2Transform xfB)
         {
             B2Polygon polygonA = b2MakeCapsule(segmentA.point1, segmentA.point2, 0.0f);
             return b2CollidePolygons(ref polygonA, xfA, ref polygonB, xfB);

src/Box2D.NET/B2Shapes.cs

@@ -1502,7 +1502,7 @@ public static void b2Shape_SetCapsule(in B2ShapeId shapeId, in B2Capsule capsule
             b2ResetProxy(world, shape, wakeBodies, destroyProxy);
         }
 
-        public static void b2Shape_SetSegment(in B2ShapeId shapeId, ref B2Segment segment)
+        public static void b2Shape_SetSegment(in B2ShapeId shapeId, in B2Segment segment)
         {
             B2World world = b2GetWorldLocked(shapeId.world0);
             if (world == null)