Not the same type of metrics, and not Rust, but C++ - but there is also https://perfetto.dev/ https://perfetto.dev/ which has custom (protobuf-based) protocol,

Not the same type of metrics, and not Rust, but C++ - but there is also https://perfetto.dev/ https://perfetto.dev/ which has custom (protobuf-based) protocol, but the generated code is not with the standard protoc, but custom one https://perfetto.dev/docs/design-docs/protozero https://perfetto.dev/docs/design-docs/protozero - with some limitations (last time I checked you can't modify fields, just add values of sorts - which makes sense in the embedded case)