This is a follow up on #7878

The variant spec states the string values in the metadata dictionary must be UTF-8 encoded strings.

We do this check here:

Since we offer simdutf8 as an optional dependency in other crates, we could do the same when performing the validation above. See @Dandandan's comment.

The rough idea being:

If simdutf8 is supported, do:

let value_str = simdutf8::basic::from_utf8(value_buffer)?;

else, default to the existing implementation