refactor(tvix/eval): use internal SourceCode field in error printers

Makes use of the SourceCode field now being stored directly in
errors (see parent CL). With this change, the default `Display`
implementation can now format errors correctly, and there is no need
to keep a `SourceCode` around just for error formatting.

Updates dependent crates (CLI, serde, tvixbolt) to use this correctly.

Change-Id: Iddc5d7a6b4bab391f30a999e4c68aca34304c059
Reviewed-on: https://cl.tvl.fyi/c/depot/+/10987
Tested-by: BuildkiteCI
Reviewed-by: flokli <flokli@flokli.de>

corp/tvixbolt/src/main.rs

@@ -323,12 +323,7 @@ fn eval(model: &Model) -> Output {
 
     if !result.errors.is_empty() {
         for error in &result.errors {
-            writeln!(
-                &mut out.errors,
-                "{}\n",
-                error.fancy_format_str(&source).trim(),
-            )
-            .unwrap();
+            writeln!(&mut out.errors, "{}\n", error.fancy_format_str().trim(),).unwrap();
         }
 
         return out;