[refactor] eval: drop batch_unit/trial_forward from remaining metrics

Completes the d1bc1413 cleanup pass on the five files that were
skipped because dataloader had pending modifications. With those
modifications now landed (commits 7cdbcc94 + c2a22560), the dead
code in optical_flow + the four aux-using vbench metrics
(color/multiple_objects/object_class/spatial_relationship) can go.

Mechanical removal of batch_unit class attrs and trial_forward
method overrides — neither is read anywhere since calibrate() was
deleted in 502f061d.

Parity verified on fs-mbz-gpu-085: byte-identical to v3 baseline.

fastvideo/eval/metrics/common/optical_flow/metric.py

@@ -251,7 +251,6 @@ class OpticalFlowMetric(BaseMetric):
     needs_gpu = True
     backbone = "optical_flow"
     dependencies = ["ptlflow"]
-    batch_unit = "frame_pair"
 
     def __init__(
         self,
@@ -284,22 +283,6 @@ class OpticalFlowMetric(BaseMetric):
         self._model.eval()
         self._model = self._model.to(self.device)
 
-    def trial_forward(self, batch_size, *, height, width, num_frames):
-        from ptlflow.utils.io_adapter import IOAdapter
-        io_adapter = IOAdapter(
-            output_stride=self._model.output_stride,
-            input_size=(height, width),
-            cuda=(self.device.type == "cuda"),
-        )
-        dummy_bgr = np.random.randint(0, 255, (height, width, 3), dtype=np.uint8)
-        pair_tensors = []
-        for _ in range(batch_size):
-            inputs = io_adapter.prepare_inputs([dummy_bgr, dummy_bgr])
-            pair_tensors.append(inputs["images"])
-        batched = torch.cat(pair_tensors, dim=0)
-        with torch.no_grad():
-            self._model({"images": batched})
-
     def _compute_flows_batched(
         self, pair_frames: list[tuple[np.ndarray, np.ndarray]], io_adapter,
     ) -> list[np.ndarray]:

fastvideo/eval/metrics/vbench/color/metric.py

@@ -26,7 +26,6 @@ class ColorMetric(BaseMetric):
     requires_reference = False
     higher_is_better = True
     needs_gpu = True
-    batch_unit = "video"
     dependencies = ["detectron2"]
 
     def __init__(self) -> None:

fastvideo/eval/metrics/vbench/multiple_objects/metric.py

@@ -20,7 +20,6 @@ class MultipleObjectsMetric(BaseMetric):
     requires_reference = False
     higher_is_better = True
     needs_gpu = True
-    batch_unit = "video"
     dependencies = ["detectron2"]
 
     def __init__(self) -> None:

fastvideo/eval/metrics/vbench/object_class/metric.py

@@ -20,7 +20,6 @@ class ObjectClassMetric(BaseMetric):
     requires_reference = False
     higher_is_better = True
     needs_gpu = True
-    batch_unit = "video"
     dependencies = ["detectron2"]
 
     def __init__(self) -> None:

fastvideo/eval/metrics/vbench/spatial_relationship/metric.py

@@ -57,7 +57,6 @@ class SpatialRelationshipMetric(BaseMetric):
     requires_reference = False
     higher_is_better = True
     needs_gpu = True
-    batch_unit = "video"
     dependencies = ["detectron2"]
 
     def __init__(self) -> None: