chore: drop redundant import deepmd.pt preloads

After 87c9f3f ``deepmd.pt_expt.utils.comm`` self-bootstraps
``libdeepmd_op_pt.so`` via ``_check_underlying_ops_loaded()``, so the
explicit ``import deepmd.pt`` preloads in conftest.py and
test_border_op_backward.py are no longer needed.

Closes 2 of the 13 GitHub Advanced Security CodeQL "unused import"
alerts on the PR. The remaining 5 Python alerts (other tests'
``import deepmd.pt_expt.utils.comm`` for opaque-op registration) and
6 C++ alerts (TORCH_LIBRARY_* / border_op_export reachable only
through macro-expanded static initialization) are CodeQL false
positives that need to be dismissed in the GitHub Security UI rather
than fixed in source.

Author: Han Wang

source/tests/pt_expt/conftest.py

@@ -17,14 +17,9 @@
     _get_current_function_mode_stack,
 )
 
-# Import ``deepmd.pt`` at conftest evaluation time so libdeepmd_op_pt.so
-# is loaded and ``deepmd_export::{border_op, border_op_backward}`` are
-# registered before any pt_expt test module imports
-# ``deepmd.pt_expt.utils`` (which transitively imports ``comm.py`` and
-# its ``_check_underlying_ops_loaded()`` runtime check). Previously this
-# worked only when collected alongside earlier tests that happened to
-# import deepmd.pt first.
-import deepmd.pt  # noqa: F401  - side-effect: register custom ops
+# ``deepmd.pt_expt.utils.comm`` self-bootstraps libdeepmd_op_pt.so via
+# ``_check_underlying_ops_loaded()``, so we no longer need to preload
+# ``deepmd.pt`` here.
 
 
 def _pop_device_contexts() -> list:

source/tests/pt_expt/utils/test_border_op_backward.py

@@ -30,9 +30,9 @@
 import pytest
 import torch
 
-# Ensure the new C++ symbol is loaded.  pt_expt imports deepmd.pt for
-# the custom-op .so.
-import deepmd.pt
+# comm self-bootstraps the underlying libdeepmd_op_pt.so when needed, so
+# this single side-effect import is enough to register both the C++
+# ops (deepmd::border_op_backward) and their fake/autograd metadata.
 import deepmd.pt_expt.utils.comm  # noqa: F401  - registers deepmd_export::border_op