Prevent Bazel lockfile non reproducibility for end users

[cerisier]

Using crate.from_specs results in non reproducible MODULE.bazel.lock between platforms for end users of the protobuf bazel module.

Using crate.from_cargo instead (which marks the crate module extension as reproducible) makes bazel skips the entry in the lockfile altogether and allows reproducible lockfiles for end users of the protobuf bazel module.

cc @fmeum

[cerisier]

I'll wait until rust is reintroduced after 29.x before fixing this then ! Thanks.

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