feat(tvix/derivation): add nix drv path generation to Derivation

This adds a function to generate the derivation path. The computation
is based on the Go implementation.

Change-Id: Iae89db4976f5fd9208f0453f73688689a245cd66
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7729
Tested-by: BuildkiteCI
Reviewed-by: flokli <flokli@flokli.de>

tvix/derivation/src/lib.rs

@@ -1,3 +1,4 @@
+mod nix_hash;
 mod output;
 mod string_escape;
 mod write;