Add sui-base workdir for selecting a "cargo binaries sui" installation

[mario4tier]

Discussed in https://github.com/sui-base/sui-base/discussions/3

Latest action items (may change):

• Add a cargobinsui cargobin workdir when detecting a Sui binary on .install and make it active (if no other workdir already active).
• Consider to detect and create the workdir (silently in background) in other places (e.g. in common script init code). * Add "asui base list" and "asui base set " to more conveniently switch workdir.

[mario4tier]

Fixed with commit 39b3679463b0820519fa033b1b9363e614fc4107, 82e1018b1f3ff2f67594c849c07c0d8a764f2a3a

[mario4tier]

This is now completed.

workdir name is "cargobin"

It is active by default on install.

There is no script (yet) to make it active "later", but it will be done as a generalization that will work with any workdir in the coming weeks (while working on devnet/tesnet).