feat(client-entity): use snapshot history for entity interpolation

Replace exponential smoothing with a buffered snapshot system. Each entity keeps a deque of position/direction snapshots with timestamps; the render transform is interpolated at a fixed 100 ms render delay to hide network jitter. Snapshots are capped to 16 entries.

include/Cubed/gameplay/ecs/client_entity.hpp

@@ -2,6 +2,8 @@
 #include "Cubed/gameplay/ecs/animation.hpp"
 #include "Cubed/gameplay/ecs/transform.hpp"
 #include "Cubed/gameplay/model.hpp"
+
+#include <deque>
 namespace Cubed {
 struct BaseClientCreature {
 
@@ -16,4 +18,14 @@ struct SoundTime {
     float next_call_time;
 };
 
+struct ClientEntitySnapshot {
+    double time_ms = 0.0;
+    glm::vec3 pos{0.0f};
+    glm::vec3 dir{0.0f};
+};
+
+struct ClientEntityState {
+    std::deque<ClientEntitySnapshot> history;
+};
+
 } // namespace Cubed

include/Cubed/tools/time_tools.hpp

@@ -4,6 +4,7 @@
 #include <cstdint>
 namespace Cubed {
 namespace Tools {
+// return ms
 inline uint64_t get_time_ticks() { return SDL_GetTicks(); }
 } // namespace Tools