chore(tvix/eval): note on context-aware hashString

It must propagate context too.

Change-Id: If57c22c9723ea02aa013f69d3dcf96054476d8de
Reviewed-on: https://cl.tvl.fyi/c/depot/+/10433
Tested-by: BuildkiteCI
Autosubmit: raitobezarius <tvl@lahfa.xyz>
Reviewed-by: tazjin <tazjin@tvl.su>

tvix/eval/src/builtins/mod.rs

@@ -588,6 +588,7 @@ mod pure_builtins {
         _algo: Value,
         _string: Value,
     ) -> Result<Value, ErrorKind> {
+        // FIXME: propagate contexts here.
         Ok(Value::Catchable(CatchableErrorKind::UnimplementedFeature(
             "hashString".to_string(),
         )))