fix(strings): reject multi-char split separators

Author: prantikmedhi

strings/split.py

@@ -17,8 +17,15 @@ def split(string: str, separator: str = " ") -> list:
 
     >>> split(";abbb;;c;", separator=';')
     ['', 'abbb', '', 'c', '']
+
+    >>> split("a--b--c", separator="--")
+    Traceback (most recent call last):
+    ValueError: separator must be a single character
     """
 
+    if len(separator) != 1:
+        raise ValueError("separator must be a single character")
+
     split_words = []
 
     last_index = 0