Before this PR freethreaded toolchains were not possible to be used,
this adds the minimum plumbing to get the things working. Coverage
support is also added.

Whilst at it:
- Add plumbing to print checksums only for a particular python version.
- Bump the remaining toolchain versions that used to use the 20241008
release
- Pass around the loaded platform list so that we are only defining
toolchains for the platforms that we have loaded the hermetic toolchain
for.

Tested:
```
$ bazel run --//python/config_settings:python_version=3.13.0 --//python/config_settings:py_freethreaded="yes" //python/private:current_interpreter_executable
...
Python 3.13.0 experimental free-threading build (main, Oct 16 2024, 03:26:14) [Clang 18.1.8 ] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>>
```

Closes bazel-contrib#2129.
Work towards bazel-contrib#2386.