Add nanobind_bazel v2.4.0

[nicholasjng]

Mirrors nanobind v2.4.0. Note that no nanobind v2.3.0 was released due to a mistake in the release process.

[nicholasjng]

I guess Bazel 6.x can go from the presubmit, but Bazel 7.x now also fails (missing --std="c++17"), which is confusing to me.

[nicholasjng]

Decided to set the test target in the presubmit to the newly exposed @nanobind_bazel//:nanobind, which was the "headline feature" for v2.4.0. This is exactly what the separate @nanobind BCR module does in its presubmit file.

(For clarification: This is an alias pointing to the @nanobind repo extension - it was there since the beginning, because it's the whole point of nanobind_bazel, but it was not accessible by downstream users until this release.)

[nicholasjng]

Do you have an idea on how to inject C++17 as a standard into the Bazel 7.x job? I don't have it in my copts / cxxopts explicitly.

Require module maintainers' approval for newly pushed changes.