ty: un-ignore parameter-already-assigned rule (part of #15187) - #15561

Describe your change

• Add an algorithm?
• Fix a bug or typo in an existing algorithm?
• Add or change doctests? -- Note: Please avoid changing both code and tests in a single pull request.
• Documentation change?

Un-ignores the parameter-already-assigned rule in pyproject.toml as part of #15187.

• In machine_learning/k_means_clust.py, cast ax to Axes3D under TYPE_CHECKING so that ax.scatter resolves 3D coordinates (xs, ys, zs) instead of 2D parameters colliding with s=100.
• Removed rules.parameter-already-assigned = "ignore" from pyproject.toml.
• All ty check diagnostics for this rule now pass cleanly.

Related issue: #15187

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: Tracking: complete the ty gradual-typing baseline (un-ignore rules; PEP 723 blocker astral-sh/ty#691) #15187.