fix(typing): un-ignore ty deprecated rule and update contextmanager annotation

[rajpreetcodes]

Describe your change

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

Contributes to #15187.

In dynamic_programming/matrix_chain_multiplication.py, annotating @contextmanager functions with -> Iterator is deprecated in Python 3.15 typeshed stubs. Updated the annotation to -> Generator[None] and un-ignored rules.deprecated in pyproject.toml.

Ran ty check --exclude-scripts locally to verify zero deprecated diagnostics remain across the repository.

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