rust: Refactor Rust impl of protover_list_supports_protocol_or_later().
This includes a subtle difference in behaviour, as in 4258f1e18, where we return
(matching the C impl's return behaviour) earlier than before if parsing failed,
saving us computation in parsing the versions into a
protover::protoset::ProtoSet.
* REFACTOR `protover::ffi::protover_list_supports_protocol_or_later()` to use
new types and methods.