refactor(tvix/eval): directly return builtin tuples from macro

All invocations of the builtin macro had to previously filter through
the `builtin_tuple` function, but it's more sensible to directly
return these from the macro.

Change-Id: I45600ba84d56c9528d3e92570461c319eea595ce
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7825
Tested-by: BuildkiteCI
Reviewed-by: flokli <flokli@flokli.de>

tvix/eval/builtin-macros/src/lib.rs

@@ -209,8 +209,8 @@ pub fn builtins(_args: TokenStream, item: TokenStream) -> TokenStream {
     }
 
     items.push(parse_quote! {
-        pub fn builtins() -> Vec<crate::Builtin> {
-            vec![#(#builtins),*]
+        pub fn builtins() -> Vec<(&'static str, Value)> {
+            vec![#(#builtins),*].into_iter().map(|b| (b.name(), Value::Builtin(b))).collect()
         }
     });