add option to disable half precision in test.py (#2507)

Co-authored-by: Glenn Jocher <glenn.jocher@ultralytics.com>

test.py

@@ -37,6 +37,7 @@ def test(data,
          plots=True,
          wandb_logger=None,
          compute_loss=None,
+         half_precision=True,
          is_coco=False):
     # Initialize/load model and set device
     training = model is not None
@@ -61,7 +62,7 @@ def test(data,
         #     model = nn.DataParallel(model)
 
     # Half
-    half = device.type != 'cpu'  # half precision only supported on CUDA
+    half = device.type != 'cpu' and half_precision  # half precision only supported on CUDA
     if half:
         model.half()