Add support for multi-arch and multi-platform cuda toolchains

[charleysaintNV]

This MR adds support for multiple architectures and multiple versions of a toolchain. Using the redis_json you can create multiple versions of a toolchain:

cuda.redist_json(
    name = "cuda_13_0_2",
    version = "13.0.2",
    platforms = [
        "linux-x86_64",
        "linux-sbsa",
    ],
)
cuda.redist_json(
    name = "cuda_13_0_0",
    version = "13.0.0",
    platforms = [
        "linux-x86_64",
        "linux-sbsa",
    ],
)
cuda.redist_json(
    name = "cuda_12_8_0",
    version = "12.8.0",
    platforms = [
        "linux-x86_64",
        "linux-sbsa",
    ],
)

cuda.toolkit(name = "cuda")
use_repo(cuda,"cuda")

then using a set of flags in .bazelrc you can control which version of the toolchain to use in a given config:

build --@rules_cuda//cuda:exec_platform="linux-x86_64"
build --@rules_cuda//cuda:target_platform="linux-x86_64"
build --@rules_cuda//cuda:version="13.0.0"

[steple]

Thanks for adding this, I think this will be very useful.

[charleysaintNV]

pushed a new commit with the versions stuff moved around and all in one place at least and I changed the name of the nvcc_platform and runtime_platform to exec and target

[cloudhan]

would a platform_mapping with attr.string_dict be better here? Validating the key in the rule impl seem to be future proof.

[cloudhan]

This is not quite true if CTK delete some component in the future. I think a union across all CTK versions will be a little bit more robust.

[charleysaintNV]

This could take some work, right now the version in cuda_toolkit isn't going to necessarily be correct since it's pointing to @cuda which can point to any number of versioned cuda repos, but I don't know if that gets used anywhere in the rules so I'll try removing it and see what falls out...

[charleysaintNV]

The logic is pretty deeply embedded in the repository rules where I can't use the value of a flag. I might need to go back and add the ability to register multiple toolkits to get everything to work as expected...

[cloudhan]

Lets leave it for future improvement, just point it out :)