Remove inline torchsim module, clean up StateDict removal

Remove the inline torchsim wrapper from metatomic-torch entirely. Engine
wrappers belong in standalone packages (metatomic-torchsim), not inside
the core package. Deletes the module, tests, tox env, and CI step.

Also cleans up the residual dict-to-SimState fallback in the standalone
package forward() method and fixes batch tests to use same-sized
supercells (the LJ test model cannot batch different-sized systems).

Author: HaoZeke

.github/workflows/torch-tests.yml

@@ -70,9 +70,9 @@ jobs:
           METATOMIC_TESTS_TORCH_VERSION: ${{ matrix.torch-version }}
           METATOMIC_TESTS_NUMPY_VERSION_PIN:  ${{ matrix.numpy-version-pin }}
 
-      - name: run torchsim wrapper tests
+      - name: run metatomic-torchsim tests
         if: matrix.python-version != '3.10'
-        run: tox -e torchsim-torch-tests
+        run: tox -e torchsim-tests
         env:
           PIP_EXTRA_INDEX_URL: https://download.pytorch.org/whl/cpu
           METATOMIC_TESTS_TORCH_VERSION: ${{ matrix.torch-version }}

python/metatomic_torch/metatomic/torch/__init__.py

@@ -70,9 +70,5 @@ def __getattr__(name):
         import metatomic.torch.ase_calculator
 
         return metatomic.torch.ase_calculator
-    elif name == "torchsim":
-        import metatomic.torch.torchsim
-
-        return metatomic.torch.torchsim
     else:
         raise AttributeError(f"module {__name__!r} has no attribute {name!r}")

python/metatomic_torch/metatomic/torch/torchsim.py

@@ -321,15 +321,10 @@ def create_version_number(version):
         "metatensor-operations >=0.4.0,<0.5",
     ]
 
-    extras_require = {
-        "torchsim": ["torch-sim-atomistic"],
-    }
-
     setup(
         version=create_version_number(METATOMIC_TORCH_VERSION),
         author=", ".join(authors),
         install_requires=install_requires,
-        extras_require=extras_require,
         ext_modules=[
             Extension(name="metatomic_torch", sources=[]),
         ],