Proofs misc setup improvements

[W95Psp]

This PR has a bunch of improvements for the F* setup.

• It's using the new Makefile I wrote for the tutorial, and that I improved yesterday evening for sandbox. Now F* caching is project-wide and should work.
• Use only one dependency, workspace-wide, to hax-lib, so that we can actually run cargo update hax-lib
• put the makefile at one place, and have proxy makefiles that just include them

[mamonet]

The output layout is much better, and rebuilding now starts where it left off.

[W95Psp]

Seems like this was merged into #475

[karthikbhargavan]

#475 is now merged.
Could you check if there were some changes here that did not make it into that PR?
Otherwise, let's close this.

[W95Psp]

Nice, let's close this, there are a few thing, gonna make another PR