Fix Boyer-Moore bad character shift having no effect

The bad_character_heuristic() reassigned the for-loop variable i
inside the loop body, which has no effect on iteration in Python.
As a result the bad-character shift was dead code and the search
degenerated into brute-force O(n*m) checking every position,
while still claiming O(n/m) in the module docstring.

Convert the loop to a while loop so the shift actually applies,
guaranteeing at least one position of progress per iteration via
max(i + 1, mismatch_index - match_index).

Verified: all doctests pass, 2000 randomized comparisons against
brute-force search pass, and the example from the issue now takes
9 iterations instead of 29.

Fixes #14844

Author: kumarsatyam9378-art

strings/boyer_moore_search.py

@@ -86,15 +86,18 @@ def bad_character_heuristic(self) -> list[int]:
         """
 
         positions = []
-        for i in range(self.textLen - self.patLen + 1):
+        i = 0
+        while i <= self.textLen - self.patLen:
             mismatch_index = self.mismatch_in_text(i)
             if mismatch_index == -1:
                 positions.append(i)
+                i += 1
             else:
                 match_index = self.match_in_pattern(self.text[mismatch_index])
-                i = (
-                    mismatch_index - match_index
-                )  # shifting index lgtm [py/multiple-definition]
+                # shift pattern so the last occurrence of the mismatched
+                # character in the pattern aligns with the text, while
+                # always making at least one position of progress
+                i = max(i + 1, mismatch_index - match_index)
         return positions