chore(tvix/cargo): add rustyline dependency

There's a few options for this, but this one seems fine in terms of
features and doesn't have an insane amount of dependencies.

Change-Id: Ief99e66bfee0ba0ba1cfdd09568b002121b7325b
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6169
Reviewed-by: grfn <grfn@gws.fyi>
Tested-by: BuildkiteCI

tvix/eval/Cargo.toml

@@ -8,6 +8,7 @@ edition = "2021"
 [dependencies]
 rnix = "0.10.2"
 smol_str = "0.1"
+rustyline = "10.0.0"
 
 [dev-dependencies]
 criterion = "0.3.6"