py_cc_toolchain should contain EXT_SUFFIX

See https://github.com/bazelbuild/bazel-central-registry/pull/4539#discussion_r2080143661 for some context.

This value is needed to create python extensions. Note that there are a few different names that can be used, for example `.so`, `.abi3.so`, and `.cpython-312-x86_64-linux-gnu.so`. The latter is preferable when not using the python limited api because it prevents runfiles conflicts between python versions properly, meaning that transitions can work without completely breaking things.

I believe for autoconfigured pythons, you could obtain this value like so:

```
❯ python -c 'import sysconfig; print(sysconfig.get_config_var("EXT_SUFFIX"))'
.cpython-312-x86_64-linux-gnu.so
```

从 py_cc_toolchain 的自动配置路径开始，并查看链接的 bazel-central-registry 讨论以了解背景。运行所示的 Python sysconfig 命令来检查 EXT_SUFFIX 值；当工具链公开适当的后缀（包括可用时完整的解释器特定形式）时，即表示完成。

由索引模型根据 Issue 内容生成。