[proc macros]: support for named parameters (JSON Map/Object)

[niklasad1]

Currently in proc macros one implementation for named parameter(s) exist here

The reason why it's not used is because it won't work to have a serde implementation inside a trait impl with generic type parameters, thus one would a get compile error such as can't use generic parameters from outer function.

The reason for this is how the RpcServer trait is generated.

pub trait RpcServer<T> {
   // defined methods without impls
   async fn foo() -> Result<(), Error>;


  ///Collects all the methods and subscriptions defined in the trait and adds them into a single `RpcModule`.
  fn into_rpc(self) -> jsonrpsee::RpcModule<Self> {
       // registering methods and decoding params goes here (which is problematic for serde impls)
  }
}

[dvdplm]

This could use a good description and a design suggestion.