build: upgrade scikit-learn>=1.9.0 and scipy>=1.18.1 specifiers (pyproject.toml only)

[priya-sundaram-dev]

Describe your change:

Bumps the minimum-version specifiers for the two scientific dependencies to their current releases:

• scikit-learn>=1.5.2 → >=1.9.0
• scipy>=1.16.2 → >=1.18.1

This keeps the floors in step with what already resolves in CI. Per @cclauss's request on #15105, this is a pyproject.toml-only change — it does not touch uv.lock (the earlier split-out PRs #15154/#15155 were auto-closed by algorithms-keeper for an unchecked checklist and for touching uv.lock, respectively).

• Add an algorithm?
• Fix a bug or typo in an existing algorithm?
• Add or change the documentation?
• Documentation change?

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: none.

[cclauss]

Nice! Thanks.