rachit-27

### Describe your change: * [ ] Add an algorithm? * [x] Fix a bug or typo in an existing algorithm? * [ ] Add or change doctests? -- Note:...

### Summary Implements the Shell Sort algorithm inside `sorts/shell_sort.py`. ### Details - Added Shell Sort function with proper docstring, type hints, and doctests. - Created corresponding unit tests under `tests/sorts/test_shell_sort.py`....