Use ty to type-check Python files (#17229)

I added mypy type‑checking in https://github.com/astral-sh/uv/pull/5332,
so I think it's a good time to switch to ty now :)

.github/workflows/ci.yml

@@ -116,7 +116,12 @@ jobs:
         run: uvx ruff check .
 
       - name: "Python type check"
-        run: uvx mypy
+        run: |
+          uvx ty check python/uv
+          uvx \
+            --directory crates/uv-python \
+            --with-requirements fetch-download-metadata.py \
+            ty check --python-version 3.13 fetch-download-metadata.py
 
       - name: "Validate project metadata"
         run: uvx --from 'validate-pyproject[all,store]' validate-pyproject pyproject.toml

pyproject.toml

@@ -92,12 +92,5 @@ version_files = [
 "Documentation" = ["documentation"]
 "Other changes" = ["__unknown__"]
 
-[tool.mypy]
-ignore_missing_imports = true
-files = [
-  "crates/uv-python/*.py",
-  "python/uv/*.py",
-]
-
 [tool.uv]
 managed = false

python/uv/_find_uv.py

@@ -94,7 +94,7 @@ def _user_scheme() -> str:
         user_scheme = sysconfig.get_preferred_scheme("user")
     elif os.name == "nt":
         user_scheme = "nt_user"
-    elif sys.platform == "darwin" and sys._framework:
+    elif sys.platform == "darwin" and sys._framework:  # ty: ignore[unresolved-attribute]
         user_scheme = "osx_framework_user"
     else:
         user_scheme = "posix_user"