refactor: b2World_Explode to use 'in' parameters

- Changed `b2World_Explode` signature to accept `B2ExplosionDef` as `in` parameter instead of `ref`.
- Updated call sites in Samples and Tests to remove `ref` keyword.
- This change optimizes performance by reducing struct copying and ensures read-only access to explosion definition data.

Author: ikpil

src/Box2D.NET.Samples/Samples/Bodies/Weeble.cs

@@ -112,7 +112,7 @@ public override void UpdateGui()
             def.radius = m_explosionRadius;
             def.falloff = 0.1f;
             def.impulsePerLength = m_explosionMagnitude;
-            b2World_Explode(m_worldId, ref def);
+            b2World_Explode(m_worldId, def);
         }
 
         ImGui.PushItemWidth(100.0f);

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

@@ -195,7 +195,7 @@ public override void UpdateGui()
             def.radius = m_explosionRadius;
             def.falloff = 0.1f;
             def.impulsePerLength = m_explosionMagnitude;
-            b2World_Explode(m_worldId, ref def);
+            b2World_Explode(m_worldId, def);
         }
 
         ImGui.SliderFloat("Magnitude", ref m_explosionMagnitude, -20.0f, 20.0f, "%.1f");

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

@@ -160,7 +160,7 @@ public override void Step()
                         explosionDef.position = data.manifold.points[0].point;
                         explosionDef.radius = 1.0f;
                         explosionDef.impulsePerLength = 20.0f;
-                        b2World_Explode(m_worldId, ref explosionDef);
+                        b2World_Explode(m_worldId, explosionDef);
 
                         b2DestroyBody(m_projectileId);
                         m_projectileId = b2_nullBodyId;

src/Box2D.NET.Samples/Samples/Joints/TopDownFriction.cs

@@ -125,7 +125,7 @@ public override void UpdateGui()
             def.radius = 10.0f;
             def.falloff = 5.0f;
             def.impulsePerLength = 10.0f;
-            b2World_Explode(m_worldId, ref def);
+            b2World_Explode(m_worldId, def);
 
             DrawCircle(m_draw, def.position, 10.0f, B2HexColor.b2_colorWhite);
         }

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

@@ -98,7 +98,7 @@ public override void UpdateGui()
             def.radius = m_radius;
             def.falloff = m_falloff;
             def.impulsePerLength = m_impulse;
-            b2World_Explode(m_worldId, ref def);
+            b2World_Explode(m_worldId, def);
         }
 
         ImGui.SliderFloat("radius", ref m_radius, 0.0f, 20.0f, "%.1f");

src/Box2D.NET.Samples/Samples/Worlds/LargeWorld.cs

@@ -224,7 +224,7 @@ public override void Step()
             def.radius = radius;
             def.falloff = 0.1f;
             def.impulsePerLength = 1.0f;
-            b2World_Explode(m_worldId, ref def);
+            b2World_Explode(m_worldId, def);
 
             m_cycleIndex = (m_cycleIndex + 1) % m_cycleCount;
         }

src/Box2D.NET/B2Worlds.cs

@@ -2449,7 +2449,7 @@ internal static bool ExplosionCallback(int proxyId, ulong userData, ref B2Explos
             return true;
         }
 
-        public static void b2World_Explode(B2WorldId worldId, ref B2ExplosionDef explosionDef)
+        public static void b2World_Explode(B2WorldId worldId, in B2ExplosionDef explosionDef)
         {
             ulong maskBits = explosionDef.maskBits;
             B2Vec2 position = explosionDef.position;

test/Box2D.NET.Test/B2WorldTest.cs

@@ -304,7 +304,7 @@ public void TestWorldCoverage()
         Assert.That(v.Y, Is.EqualTo(g.Y));
 
         B2ExplosionDef explosionDef = b2DefaultExplosionDef();
-        b2World_Explode(worldId, ref explosionDef);
+        b2World_Explode(worldId, explosionDef);
 
         b2World_SetContactTuning(worldId, 10.0f, 2.0f, 4.0f);