Timsort.py gets IndexError on larger arrays

Also left and right seem to be swapped, result works just nomenclature.

> len1, len2 = m - l + 1, r - m
> if l + len1 > len(arr):
> len1 = len(arr) - l

Start with Timsort.py and inspect the merge logic around the len1 and len2 calculations shown in the report. Reproduce the failure with a larger array, then verify that the adjusted bounds prevent IndexError and that the resulting array remains sorted.

Written by the indexing model from the issue text.