fix: GDExtension C++ build — fix enum bitwise cast, add .gdextension entry file

gdextension/simulation.gdextension

@@ -0,0 +1,8 @@
+[configuration]
+entry_symbol = "gdextension_init"
+compatibility_minimum = "4.2"
+
+[libraries]
+linux.x86_64 = "res://gdextension/simulation/gdextension/bin/linux/libsimulation.so"
+windows.x86_64 = ""
+macos.universal = ""

gdextension/simulation/src/entity.cpp

@@ -54,7 +54,7 @@ EntitySnapshot Entity::capture_snapshot() const {
 }
 
 EntitySnapshot::ChangeMask Entity::compute_change_mask(const EntitySnapshot &base) const {
-    EntitySnapshot::ChangeMask mask = EntitySnapshot::CHANGED_NONE;
+    uint32_t mask = EntitySnapshot::CHANGED_NONE;
 
     if (position_ != base.position)          mask |= EntitySnapshot::CHANGED_POSITION;
     if (velocity_ != base.velocity)          mask |= EntitySnapshot::CHANGED_VELOCITY;
@@ -67,7 +67,7 @@ EntitySnapshot::ChangeMask Entity::compute_change_mask(const EntitySnapshot &bas
     if (last_input_.input_sequence != base.last_processed_input)
         mask |= EntitySnapshot::CHANGED_INPUT;
 
-    return mask;
+    return static_cast<EntitySnapshot::ChangeMask>(mask);
 }
 
 // ---- GDScript Bindings -------------------------------------------------------