refactor(tvix/eval): remove unnecessary clones in compiler

There's basically nothing that needs *ownership* of an AST
node (which is just a little box full of references to other things
anyways), so we can thread this through as references all the way.

Change-Id: I35a1348a50c0e8e07d51dfc18847829379166fbf
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6853
Tested-by: BuildkiteCI
Reviewed-by: grfn <grfn@gws.fyi>

tvix/eval/src/eval.rs

@@ -60,7 +60,7 @@ pub fn interpret(code: &str, location: Option<PathBuf>, options: Options) -> Eva
 
     let result = if options.dump_bytecode {
         crate::compiler::compile(
-            root_expr,
+            &root_expr,
             location,
             file.clone(),
             global_builtins(),
@@ -68,7 +68,7 @@ pub fn interpret(code: &str, location: Option<PathBuf>, options: Options) -> Eva
         )
     } else {
         crate::compiler::compile(
-            root_expr,
+            &root_expr,
             location,
             file.clone(),
             global_builtins(),