Fix Boyer-Moore bad character shift having no effect

[satyamkumar-builds]

Describe your change:

In strings/boyer_moore_search.py, bad_character_heuristic() reassigned the for-loop variable i inside the loop body:

for i in range(self.textLen - self.patLen + 1):
    ...
    i = (mismatch_index - match_index)  # no effect on iteration

In Python, reassigning the loop variable does not change the iteration, so the bad-character shift was dead code. The search checked every position sequentially — brute-force O(n·m) — while the module docstring advertises Boyer-Moore O(n/m).

Fix: convert the loop to a while loop so the shift actually applies, using i = max(i + 1, mismatch_index - match_index) to guarantee forward progress (the max also covers the case where the mismatched character is absent from the pattern, where match_index == -1 makes the raw difference negative or a no-op shift).

Verification:

• All doctests pass.
• 2000 randomized text/pattern comparisons against brute-force search: identical results.
• The reproduction from the issue (text='ABCDEFGHIJKLMNOP...', pattern='MNOP') now takes 9 iterations instead of 29.

Fixes #14844

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• Does your submission pass tests?