✨: add HasArraySub protocol to support subtraction operator for array classes

Author: nstarman

src/array_api_typing/_array.py

@@ -76,11 +76,30 @@ def __add__(self, other: Self | int | float, /) -> Self:
         ...
 
 
+class HasArraySub(Protocol):
+    """Protocol for array classes that support the subtraction operator."""
+
+    def __sub__(self, other: Self | int | float, /) -> Self:
+        """Calculates the difference for each element of an array instance with the respective element of the array other.
+
+        The result of self_i - other_i must be the same as self_i + (-other_i) and must be governed by the same floating-point rules as addition (see array.__add__()).
+
+        Args:
+            other: subtrahend array. Must be compatible with self (see Broadcasting). Should have a numeric data type.
+
+        Returns:
+            an array containing the element-wise differences. The returned array must have a data type determined by Type Promotion Rules.
+
+        """  # noqa: E501
+        ...
+
+
 class Array(
     HasArrayNamespace[NS_co],
     HasArrayPos,
     HasArrayNeg,
     HasArrayAdd,
+    HasArraySub,
     Protocol,
 ):
     """Array API specification for array object attributes and methods."""