refactor(tvix/eval): remove code and location from struct

Instead, it's passed in the evaluate/compile_only functions, which feels
more naturally. It lets us set up the Evaluation struct long before
we actually feed it with data to evaluate.

Now that Evaluation::new() would be accepting an empty list of
arguments, we can simply implement Default, making things a bit more
idiomatic.

Change-Id: I4369658634909a0c504fdffa18242a130daa0239
Reviewed-on: https://cl.tvl.fyi/c/depot/+/10475
Tested-by: BuildkiteCI
Reviewed-by: tazjin <tazjin@tvl.su>
Autosubmit: flokli <flokli@flokli.de>

tvix/glue/benches/eval.rs

@@ -26,7 +26,7 @@ fn interpret(code: &str) {
     // TODO: this is a bit annoying.
     // It'd be nice if we could set this up once and then run evaluate() with a
     // piece of code. b/262
-    let mut eval = tvix_eval::Evaluation::new_impure(code, None);
+    let mut eval = tvix_eval::Evaluation::new_impure();
 
     let known_paths: Rc<RefCell<KnownPaths>> = Default::default();
     add_derivation_builtins(&mut eval, known_paths.clone());
@@ -47,7 +47,7 @@ fn interpret(code: &str) {
         ),
     ));
 
-    let result = eval.evaluate();
+    let result = eval.evaluate(code, None);
 
     assert!(result.errors.is_empty());
 }