Stubs: no two stub paths may differ only by case (Shadow vs shadow breaks macOS/Windows) #44

Reported by pythonx-compose (#12). The Compose 1.11.1 stub set contains both androidx/compose/ui/graphics/shadow/__init__.pyi (a Kotlin package) and androidx/compose/ui/graphics/Shadow/__init__.pyi (a class module). On case-insensitive filesystems (macOS default, Windows) they collide: gh run download stops extracting after 136 of 246 files, mypy reports import-not-found, and an IDE on macOS cannot see both. PythonStubsTask only warns today.

Decided: stub layout must be case-unique. A class (or object) that the runtime exposes as a module under a parent package is emitted in the parent package's __init__.pyi (as the class), and gets its own <Class>/__init__.pyi only when that path does not collide case-insensitively with a sibling. The runtime import path is unchanged; only the stub layout changes, and the mypy consumer check must still resolve from androidx.compose.ui.graphics import Shadow and the shadow package.

Completion: generating Compose 1.11.1 stubs produces no two paths equal under casefold (test asserts it); the stubs artifact extracts fully with gh run download on macOS; tools/stubs/check-stubs.sh passes on macOS without the import ignore; the CI job may move back to (or add) macOS.