feat: Switch type checker from mypy to ty

[fujikosu]

Purpose

Migrate the type checking tooling from mypy to ty, an extremely fast Python type checker by Astral (creators of ruff and uv). ty is integrated as a VS Code extension for real-time editor feedback, replacing the mypy VS Code extension.

Key decisions:

• ty replaces mypy as the VS Code type checker extension (astral-sh.ty replaces ms-python.mypy-type-checker)
• ty's language server replaces Pylance's (python.languageServer: "None"), which is ty's default recommended setup
• ty is not added to CI or pre-commit hooks because it is still pre-1.0 with no stable API (milestones), meaning diagnostics may change between versions
• Once ty stabilizes, the plan is to run it in CI in non-strict mode (default rule set) to catch real type errors without requiring full annotation coverage

Changes

Type checker migration (mypy → ty)

• Replaced ms-python.mypy-type-checker extension with astral-sh.ty in all 3 devcontainer.json files
• Replaced mypy-type-checker.importStrategy setting with ty.importStrategy and python.languageServer: "None"
• Replaced mypy==1.20.0 with ty==0.0.29 in all devcontainer pyproject.toml files
• Regenerated all 3 uv.lock files to remove mypy and add ty
• Updated .gitignore, .dockerignore, .amlignore: .mypy_cache → .ty_cache

README updates

• Added ty type checking rationale with links to version policy and milestones
• Added Future Roadmap item for ty CI/pre-commit integration once stable

Does this introduce a breaking change?

• Yes
• No

Author pre-publish checklist

• No PII in logs or output
• Made corresponding changes to the documentation
• All new packages used are included in pyproject.toml
• Functions use type hints, and there are no type hint errors

Pull Request Type

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Documentation content changes
• Experiment notebook

[Copilot]

Pull request overview

Migrates the repository’s developer type-checking experience from mypy to Astral’s ty, aligning the devcontainers and documentation with ty’s VS Code extension + language server workflow.

Changes:

• Replace the mypy VS Code extension with astral-sh.ty and configure devcontainers to disable the Python extension language server (python.languageServer: "None").
• Swap mypy==1.20.0 for ty==0.0.29 in devcontainer pyproject.toml files and regenerate corresponding uv.lock files.
• Update ignore rules and documentation to reference ty cache/files and planned future CI integration.

Reviewed changes

Copilot reviewed 10 out of 14 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/sample_pytorch_gpu_project/.devcontainer/uv.lock	Removes mypy (and related deps) and adds ty to dev dependencies lock.
src/sample_pytorch_gpu_project/.devcontainer/pyproject.toml	Replaces mypy with ty in the dev dependency group.
src/sample_pytorch_gpu_project/.devcontainer/devcontainer.json	Switches VS Code extension to astral-sh.ty and sets python.languageServer to None with ty.importStrategy.
src/sample_pytorch_gpu_project/.amlignore	Replaces .mypy_cache ignore with .ty_cache.
src/sample_cpu_project/.devcontainer/uv.lock	Removes mypy (and related deps) and adds ty to dev dependencies lock.
src/sample_cpu_project/.devcontainer/pyproject.toml	Replaces mypy with ty in the dev dependency group.
src/sample_cpu_project/.devcontainer/devcontainer.json	Switches VS Code extension to astral-sh.ty and sets python.languageServer to None with ty.importStrategy.
src/.amlignore	Replaces .mypy_cache ignore with .ty_cache.
README.md	Documents ty rationale and adds roadmap note for future CI/pre-commit integration once stable.
notebooks/.devcontainer/uv.lock	Removes mypy (and related deps) and adds ty to dev dependencies lock.
notebooks/.devcontainer/pyproject.toml	Replaces mypy with ty in the dev dependency group.
notebooks/.devcontainer/devcontainer.json	Switches VS Code extension to astral-sh.ty and sets python.languageServer to None with ty.importStrategy.
.gitignore	Replaces mypy ignores with .ty_cache/.
.dockerignore	Replaces .mypy_cache ignore with .ty_cache.

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