Fix merge sort comparable clean

[kadubhumika]

Description

Makes merge_sort.py support any comparable items instead of only relying on untyped lists.

Changes:

• Added a Comparable protocol
• Added a bounded TypeVar
• Updated merge_sort() to use generic type hints
• Added doctests for strings and floats

Part of #15234

Checklist

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized.
• I know that pull requests will not be merged if they fail the automated tests.
• This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
• All new Python files are placed inside an existing directory.
• [] All filenames are in all lowercase characters with no spaces or dashes.
• All functions and variable names follow Python naming conventions.
• All function parameters and return values are annotated with Python type hints.
• All functions have doctests that pass the automated testing.
• All new algorithms include at least one URL that points to Wikipedia or another similar explanation.
• If this pull request resolves one or more open issues, then the description above includes the issue number(s) with a closing keyword: "Fixes #ISSUE-NUMBER".

[kadubhumika]

Hi! The PR is ready for review. The latest changes have been pushed and the pre-commit checks are passing. The remaining workflows are currently awaiting maintainer approval. Thank you!

[cclauss]

@priya-sundaram-dev, your review, please.

[priya-sundaram-dev]

Thanks @kadubhumika — the merge_sort.py change itself looks good. The Comparable protocol with just __lt__, the PEP 695 merge_sort[T: Comparable] generic, and the switch to a strict < comparison (which keeps the sort stable and only depends on the one dunder the protocol declares) are all consistent. I verified it against ints, floats, and strings and the doctests pass.

One thing to fix before this can go in: the diff also touches DIRECTORY.md with a bunch of unrelated machine-learning / physics / neural-network entries. Those aren't part of this change — they're an artifact of the branch being behind master. Could you sync your branch with upstream master and revert DIRECTORY.md so this PR only touches sorts/merge_sort.py? (The checklist item "This PR only changes one algorithm file" is what the maintainers look for.) Once DIRECTORY.md is clean this is good to go from my side.

[cclauss]

It is important to always refresh your master branch before creating each new pull request.