feat(tvix/eval): check in generated project skeleton

Change-Id: Iecc8283abb289de71f22076fd88892f6ded99cb3
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6062
Tested-by: BuildkiteCI
Reviewed-by: grfn <grfn@gws.fyi>

tvix/eval/src/main.rs

@@ -0,0 +1,3 @@
+fn main() {
+    println!("Hello, world!");
+}