rearrange some sources

Sources/Voxelotl/Common/FPSCalculator.swift

@@ -0,0 +1,20 @@
+import Foundation
+
+public struct FPSCalculator {
+  private var _accumulator = Duration.zero
+  private var _framesCount = 0
+
+  public mutating func frame(deltaTime: Duration, result: (_ fps: Int) -> Void) {
+    self._framesCount += 1
+    self._accumulator += deltaTime
+
+    if self._accumulator >= Duration.seconds(1) {
+      result(self._framesCount)
+
+      self._framesCount = 0
+      self._accumulator = .init(
+        secondsComponent: 0,
+        attosecondsComponent: self._accumulator.components.attoseconds)
+    }
+  }
+}