CommonsBase_Dk

CommonsBase_Dk now carries the bootstrap split for dk0 packaging.

Implemented here:

• a source-bundle pin for the latest MlFront release tarball
• a CommonsBase_Dk.Dk0.DuneCache@2.4.2 package that repackages that tarball into a reusable zip artifact for all supported slots
• a CommonsBase_Dk.Dk0@2.4.2 recipe that stages the cache, runs a concrete dune build, and installs bin/dk0.exe for Windows x86_64 only

Still pending:

• the executable package for non-Windows_x86_64 slots
• validation of the toolchain/dependency bootstrap on real runners

Package targets in this repo:

• CommonsBase_Dk.Dk0.DuneCache@2.4.2
• CommonsBase_Dk.Dk0@2.4.2