Fix support for bazel >= 8

[traversaro]

Fix #207 .

The two modifications are:

• Add common --repo_contents_cache='' in .bazelrc to workaround In-project --output_user_root triggers the repo contents cache error, even though the target directory is excluded with .bazelignore bazelbuild/bazel#26384
• Add direct platform dependency in main MODULE.bazel, apparently in Bazel 8 it is not sufficient to have that in the tests/MODULE.bazel

[traversaro]

Add common --repo_contents_cache='' in .bazelrc to workaround

This does not work as --repo_contents_cache is not an option in Bazel 7. So I switched to disable directly the repo cache with common --repository_cache='', as that option is supported also in Bazel 7. The solution is not perfect as it disable the repository_cache also on Bazel 7 and for non-pixi users of Bazel, but I can't find a better solution (probably also I am not a big expert of Bazel), see also the upstream issue bazelbuild/bazel#24043 .

[traversaro]

@jchnmck @wep21 as I guess you may be interested in bazel integration, are you interesting in double checking this PR? Thanks!