Support PEP 739 (build-details.json)

I came across PEP 739 (https://peps.python.org/pep-0739/), which says that, starting in Python 3.14, there will be a build-details.json that gives information about the Python runtime.

There's a variety of things in it. Most of them are relevant to defining a toolchain.

For local toolchains, it looks like it can be used to get the necessary information for the toolchain _without_ running Python.

For remote toolchains, it seems less useful, but there's some info that might still be helpful. It's less useful because things like e.g. Python version have to be known before the repo that triggers a download is referenced. Populating the abi flags some of that lower level info would still be helpful, though.

* language.version_info -- Tells which Python versio
* abi.flags, extension_suffix, implementation
* libpython
* c_api

まず PEP 739 を読み、現在の rules_python ツールチェーンの動作を確認します。特に、ローカルランタイムとリモートランタイムがどのように記述されているかを確認してください。サポートすべき build-details.json のフィールドと、それらが各ツールチェーンモードにどのように対応付けられるかを明確にします。done には、合意したスコープと対応する検証を含める必要があります。

索引モデルが issue の本文から書いたものです。