Expose `sysconfig` variables in `PyRuntimeInfo` provider

# 🚀 feature request

Downstream rules are potentially interested in the selected toolchains configuration.
Specifically, building C extension modules depends on things like `EXT_SUFFIX` to create proper extensions supporting the chosen interpreter.
Because that suffix ends up in file names, downstream rules may need that value at configure time, when they can't query the interpreter.
But the `@rules_python` `repository_rule` can easily determine these variables before configure time, for each registered toolchain.

This is related to:
- https://github.com/bazelbuild/rules_python/issues/824
- https://github.com/nicholasjng/nanobind-bazel/issues/61
- I'm sure other downstream bazel tooling related to C extensions would like this as-well

### Relevant Rules

This feature would ultimately need changes to:
- `PyRuntimeInfo` (basic schema)
- `py_runtime` (so that third party toolchains/interpreters can provide that information too)
- the internal pluming providing the `@rules_python` provided internal toolchains

### Description

`PyRuntimeInfo` needs a field `ext_suffix`, or alternatively `sysconfig_variables` (for future extension).
At extension instantiation time, when setting up the toolchain repos, the respective interpreters should be queried for their `ext_suffix`; alternatively, that information could be determined offline.

从 PyRuntimeInfo schema 和 issue 中提到的 py_runtime 规则开始，然后追踪提供已注册解释器的内部 toolchain repository 设置。参考 issues #824 和 nanobind-bazel#61 了解背景；当 ext_suffix 等 sysconfig 数据可供下游规则使用，并且可以由第三方 toolchain 提供时，即视为完成。

由索引模型根据 Issue 内容生成。