Tracking of dependencies for releasing to opam

[mbarbin]

This issue tracks the dependencies that would need to be handled first in order to publish vcs to opam. Resolution may for example be any of:

• Refactor vcs to remove the dependency
• Vendor it in vcs
• Publish the dependency itself into opam
• ?

For the library part (vcs, vcs-git)

• eio-process => vendored => removed
• fpath-base => release status
• provider => released
• union-find => vendored => removed

Command line interface (ocaml-vcs)

To include the command line interface (e.g, for quick exploratory tests):

• command-unix-for-opam => switched to cmdlang
• eio-writer => vendored => removed
• cmdlang

[mbarbin]

Re: union-find. I tried vendoring it into vcs but this currently creates other issues for me. Work in progress and issue tracking ocaml/dune#10268.