Take a look at how it is done in [PMS](https://github.com/software-mansion/scarb/blob/d22d0e0fb0429ae5924c51e6ecd7b1b5fea47034/scarb/src/ops/proc_macro_server/mod.rs#L85). Notice that all the logic is implemented in the [Handler](https://github.com/software-mansion/scarb/blob/d22d0e0fb0429ae5924c51e6ecd7b1b5fea47034/scarb/src/ops/proc_macro_server/methods/mod.rs#L14) trait
