test(sampler): drain resumed trillion-frame sampler via iter() to avoid list() prealloc

list(sampler) calls PyObject_LengthHint -> __len__ (the full 10**12 epoch length) and
preallocates that many slots before iterating, OOMing even though the resumed epoch only
yields 3 frames. Collect through the iterator (no length hint) so the test exercises the
real O(1) seek/drain instead of CPython's list growth heuristic.

tests/datasets/test_sampler.py

@@ -246,7 +246,10 @@ def test_deterministic_sampler_constant_memory():
     sampler = deterministic_sampler([0], [num_frames], shuffle=True, seed=0)
     assert len(sampler) == num_frames
     sampler.load_state_dict({"epoch": 3, "start_index": num_frames - 3})
-    tail = list(sampler)
+    # Collect via the iterator: list(sampler) would call PyObject_LengthHint -> sampler.__len__
+    # (the full epoch length, here 10**12) and pre-allocate that many slots before iterating. The
+    # iterator itself exposes no length hint, so this stays O(1) like the resumed epoch it drains.
+    tail = list(iter(sampler))
     assert len(tail) == 3
     assert all(0 <= idx < num_frames for idx in tail)