[ci] use libra-cli bin for faster CI runs

[0o-de-lally]

CI was using different binaries and rebuilding some more. This simplifies so all tests can use a pre-build libra-cli binary, published in this repo.

• [x] CI runs were previously building the move compiler. libra move framework fixes so that the bin can compile Move on any directory
• [x] It also downloaded a diem-node binary. Changes to libra api made it compatilble for purposes of diem-forge
• [x] have the libra-cli download be separate from env building
• [x] add the github workspace and libra to the $PATH for GH env.

[0o-de-lally]

Pro tip for situations like this: have the downloaded binary print its version to the log. That way if there's some confusion later about which version was used in this job run, it's easy to tell.

Good one. Will do that now