feat: Add GLSL renderer and implement FPS overlay across rendering backends

Signed-off-by: Hans Kokx <hans.d.kokx@gmail.com>

packages/wolf_3d_dart/lib/src/engine/wolf_3d_engine_base.dart

@@ -74,6 +74,12 @@ class WolfEngine {
   /// Elapsed engine lifetime in milliseconds.
   int get timeAliveMs => _timeAliveMs;
 
+  /// Exponential moving average of rendered frames per second.
+  double _smoothedFps = 0.0;
+
+  /// Current smoothed FPS, suitable for lightweight on-screen diagnostics.
+  double get fps => _smoothedFps;
+
   /// The episode index where the game session begins.
   final int? startingEpisode;
 
@@ -203,6 +209,14 @@ class WolfEngine {
 
     // Trust the incoming delta time natively
     _timeAliveMs += delta.inMilliseconds;
+    if (delta.inMicroseconds > 0) {
+      final double instantaneousFps = 1000000.0 / delta.inMicroseconds;
+      if (_smoothedFps <= 0.0) {
+        _smoothedFps = instantaneousFps;
+      } else {
+        _smoothedFps = (_smoothedFps * 0.88) + (instantaneousFps * 0.12);
+      }
+    }
 
     // 1. Process User Input
     input.update();