test: add doctest exercising multi-position bad-character shift

Addresses reviewer feedback by adding a test case where the pattern
'MNOP' is searched in a 32-character text, verifying correct match
positions [12, 28] and demonstrating that the bad-character shift
skips multiple positions at once.

Author: almogyalin

strings/boyer_moore_search.py

@@ -116,6 +116,14 @@ def bad_character_heuristic(self) -> list[int]:
         >>> bms = BoyerMooreSearch(text="ABAABA", pattern="AB")
         >>> bms.bad_character_heuristic()
         [0, 3]
+
+        Example where the bad-character shift skips multiple positions at once:
+
+        >>> bms = BoyerMooreSearch(
+        ...     text="ABCDEFGHIJKLMNOPABCDEFGHIJKLMNOP", pattern="MNOP"
+        ... )
+        >>> bms.bad_character_heuristic()
+        [12, 28]
         """
 
         positions = []