Make available imports in graphnet.data.{sqlite,parquet} conditional on whether 'torch' is installed

Author: asogaard

src/graphnet/data/parquet/__init__.py

@@ -1,2 +1,8 @@
+from graphnet.utilities.imports import has_torch_package
+
 from .parquet_dataconverter import ParquetDataConverter
-from .parquet_dataset import ParquetDataset
+
+if has_torch_package():
+    from .parquet_dataset import ParquetDataset
+
+del has_torch_package

src/graphnet/data/sqlite/__init__.py

@@ -1,4 +1,10 @@
+from graphnet.utilities.imports import has_torch_package
+
 from .sqlite_dataconverter import SQLiteDataConverter
-from .sqlite_dataset import SQLiteDataset
-from .sqlite_dataset_perturbed import SQLiteDatasetPerturbed
 from .sqlite_utilities import run_sql_code, save_to_sql
+
+if has_torch_package():
+    from .sqlite_dataset import SQLiteDataset
+    from .sqlite_dataset_perturbed import SQLiteDatasetPerturbed
+
+del has_torch_package