Gradle plugin: expose per-target CPython include directories as a public Provider #46

What

The Gradle plugin should publish, for each target, the include directory of the CPython it downloads. Each value is a Provider<Directory> keyed by target and flavour; free-threaded is a separate key. The task that extracts the tree comes along as the provider's task dependency. pypackpack's compile slot (TypedPython M3, #25) takes these as input.

Current locations, from the build-time acquisition tree python-multiplatform/build/python-standalone/extracted/:

Why

A TypedPython extension has to be compiled against the headers, ABI tag and flavour of the CPython the app embeds, not the host Python. Compilation happens at build time, so what is staged into PYTHONHOME does not matter here. The paths must be exposed as public build outputs, not hard-coded.

Owner

The leader.

Done when

A plugin test resolves the include provider for each target. Each one contains Python.h, and the free-threaded one is distinct from the default one. Resolving a provider runs the extraction task.