Content-addressed Nix derivations test
now i can finally build my fucking local projects reasonably, supposedly
$ ./demo.bash
-- default
++ dir1/non-can.nix
/nix/store/r6j9ga1g1i7gvsfs8fxrz68vba0pq5x3-can-test-101
++ dir2/non-can.nix
/nix/store/zsibdfa20wbw34a6s0syfhlq4q5cvjl6-can-test-101
-- ca
++ dir1/can.nix
/nix/store/9sjsq70p2aa57m56mb3qg9x9i2hl5jw0-can-test-101
++ dir2/can.nix
/nix/store/9sjsq70p2aa57m56mb3qg9x9i2hl5jw0-can-test-101