chore: initialise extension file to prevent build failure

pydatastructs/graphs/__init__.py

@@ -6,6 +6,9 @@
 )
 __all__.extend(graph.__all__)
 
+from . import _extensions
+
+
 from . import algorithms
 from . import adjacency_list
 from . import adjacency_matrix

pydatastructs/linear_data_structures/__init__.py

@@ -6,6 +6,8 @@
     algorithms,
 )
 
+from . import _extensions
+
 from .arrays import (
     OneDimensionalArray,
     DynamicOneDimensionalArray,

pydatastructs/miscellaneous_data_structures/__init__.py

@@ -8,6 +8,8 @@
     sparse_table,
 )
 
+from . import _extensions
+
 from .binomial_trees import (
     BinomialTree
 )

pydatastructs/trees/__init__.py

@@ -7,6 +7,9 @@
     heaps,
 )
 
+from . import _extensions
+
+
 from .binary_trees import (
     BinaryTree,
     BinarySearchTree,

pydatastructs/utils/__init__.py

@@ -5,6 +5,8 @@
     testing_util,
 )
 
+from . import _extensions
+
 from .misc_util import (
     TreeNode,
     MAryTreeNode,