refactor: b2CreateChain API to use 'in' parameter

- Changed `b2CreateChain` signature to accept `B2ChainDef` as `in` parameter instead of `ref`.
- Updated internal implementation to use `ref readonly` for accessing `materials` and `points` from the definition, ensuring efficiency and safety.
- Updated all call sites in Samples and Benchmarks to remove the `ref` keyword.

Author: ikpil

src/Box2D.NET.Samples/Samples/Characters/Mover.cs

@@ -142,7 +142,7 @@ public Mover(SampleContext context) : base(context)
             chainDef.count = count;
             chainDef.isLoop = true;
 
-            b2CreateChain(groundId1, ref chainDef);
+            b2CreateChain(groundId1, chainDef);
         }
 
         B2BodyId groundId2;
@@ -172,7 +172,7 @@ public Mover(SampleContext context) : base(context)
             chainDef.count = count;
             chainDef.isLoop = true;
 
-            b2CreateChain(groundId2, ref chainDef);
+            b2CreateChain(groundId2, chainDef);
         }
 
         {

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

@@ -229,7 +229,7 @@ void Create(int index)
             chainDef.points = points;
             chainDef.count = 4;
             chainDef.isLoop = true;
-            b2CreateChain(m_bodyIds[m_bodyIndex], ref chainDef);
+            b2CreateChain(m_bodyIds[m_bodyIndex], chainDef);
         }
 
         m_bodyIndex = (m_bodyIndex + 1) % e_maxCount;

src/Box2D.NET.Samples/Samples/Continuous/ChainDrop.cs

@@ -48,7 +48,7 @@ public ChainDrop(SampleContext context) : base(context)
         chainDef.count = 4;
         chainDef.isLoop = true;
 
-        b2CreateChain(groundId, ref chainDef);
+        b2CreateChain(groundId, chainDef);
 
         m_bodyId = b2_nullBodyId;
         m_yOffset = -0.1f;

src/Box2D.NET.Samples/Samples/Continuous/ChainSlide.cs

@@ -66,7 +66,7 @@ public ChainSlide(SampleContext context) : base(context)
             chainDef.count = count;
             chainDef.isLoop = true;
 
-            b2CreateChain(groundId, ref chainDef);
+            b2CreateChain(groundId, chainDef);
         }
 
         {

src/Box2D.NET.Samples/Samples/Continuous/GhostBumps.cs

@@ -113,7 +113,7 @@ void CreateScene()
             chainDef.materials = new[] { material };
             chainDef.materialCount = 1;
 
-            b2CreateChain(m_groundId, ref chainDef);
+            b2CreateChain(m_groundId, chainDef);
         }
         else
         {

src/Box2D.NET.Samples/Samples/Continuous/Pinball.cs

@@ -57,7 +57,7 @@ public Pinball(SampleContext context) : base(context)
             chainDef.points = vs;
             chainDef.count = 5;
             chainDef.isLoop = true;
-            b2CreateChain(groundId, ref chainDef);
+            b2CreateChain(groundId, chainDef);
         }
 
         // Flippers

src/Box2D.NET.Samples/Samples/Events/ContactEvent.cs

@@ -61,7 +61,7 @@ public ContactEvent(SampleContext context) : base(context)
             chainDef.points = points;
             chainDef.isLoop = true;
 
-            b2CreateChain(groundId, ref chainDef);
+            b2CreateChain(groundId, chainDef);
         }
 
         // Player

src/Box2D.NET.Samples/Samples/Events/FootSensor.cs

@@ -67,7 +67,7 @@ public FootSensor(SampleContext context) : base(context)
             chainDef.isLoop = false;
             chainDef.enableSensorEvents = true;
 
-            b2CreateChain(groundId, ref chainDef);
+            b2CreateChain(groundId, chainDef);
         }
 
         {

src/Box2D.NET.Samples/Samples/Events/PersistentContact.cs

@@ -51,7 +51,7 @@ public PersistentContact(SampleContext context) : base(context)
             chainDef.count = 22;
             chainDef.isLoop = true;
 
-            b2CreateChain(groundId, ref chainDef);
+            b2CreateChain(groundId, chainDef);
         }
 
         {

src/Box2D.NET.Samples/Samples/Events/SensorFunnel.cs

@@ -114,7 +114,7 @@ public SensorFunnel(SampleContext context) : base(context)
             chainDef.isLoop = true;
             chainDef.materials = [material];
             chainDef.materialCount = 1;
-            b2CreateChain(groundId, ref chainDef);
+            b2CreateChain(groundId, chainDef);
 
             float sign = 1.0f;
             float y = 14.0f;