Pin ty to available version and refresh lockfile

[thibaudcolas]

Motivation

• Replace references to mypy with the new static checker ty across the project and make dependency resolution succeed.
• Ensure developer tooling and documentation point to the actual, installable ty version used in CI and local development.

Description

• Updated pyproject.toml dev dependency to pin ty==0.0.8 and removed the mypy entries.
• Removed the [tool.mypy] configuration block from pyproject.toml and updated Makefile to run ty check instead of mypy **/*.py.
• Replaced documentation references from mypy to ty in README.md and docs/README.md.
• Regenerated uv.lock to reflect the removal of mypy and the addition of ty.

Testing

• Ran uv lock initially which failed due to unsatisfiable requirements for the previously requested ty constraint.
• After pinning ty==0.0.8, ran uv lock again which succeeded and updated uv.lock to include ty and remove mypy.
• No unit test suite was executed as part of this change; the change focused on dependency resolution and lockfile refresh.

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Codex Task