feat(tvix/eval): implement serde::Deserialize for Value

Co-Authored-By: Vincent Ambo <tazjin@tvl.su>

Change-Id: Ib6f7d1f4f4faac36b44f5f75cccc57bf912cf606
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7626
Reviewed-by: tazjin <tazjin@tvl.su>
Tested-by: BuildkiteCI

tvix/eval/src/builtins/mod.rs

@@ -339,8 +339,8 @@ mod pure_builtins {
     #[builtin("fromJSON")]
     fn builtin_from_json(_: &mut VM, json: Value) -> Result<Value, ErrorKind> {
         let json_str = json.to_str()?;
-        let json: serde_json::Value = serde_json::from_str(&json_str)?;
-        json.try_into()
+
+        serde_json::from_str(&json_str).map_err(|err| err.into())
     }
 
     #[builtin("genericClosure")]