Apply ruff==0.9.0 formatting (#13486)

* Refactor code for speed and clarity

* Auto-format by https://ultralytics.com/actions

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Co-authored-by: UltralyticsAssistant <web@ultralytics.com>

utils/segment/loss.py

@@ -61,8 +61,7 @@ class ComputeLoss:
             b, a, gj, gi = indices[i]  # image, anchor, gridy, gridx
             tobj = torch.zeros(pi.shape[:4], dtype=pi.dtype, device=self.device)  # target obj
 
-            n = b.shape[0]  # number of targets
-            if n:
+            if n := b.shape[0]:
                 pxy, pwh, _, pcls, pmask = pi[b, a, gj, gi].split((2, 2, 1, self.nc, nm), 1)  # subset of predictions
 
                 # Box regression