Allow generalising over RPC implementation (#634)

* WIP generalising RPC client

* WIP: non-object-safe RpcClientT.. aah generics everywhere

* WIP object-safe RpcClientT trait and no more extra generics

* Get core things compiling again with object-safe RpcClientT trait

* Make jsonrpsee optional and get test-runtime working again

* cargo fmt

* add RpcParams object to enforce correct formatting of rps params

* Wee tweaks

* clippy fixes

* cargo fmt

* TWeak a few types

* make sure we get jsonrpsee-types, too

* Add examples for rpc_params/RpcParams

* more doc tweaks

* remove a now unneeded dev note

* Option<Box<RawValue>> instead to avoid allocations in some cases

* update docs

* tweak RpcClientT trait docs

* Tweak docs around RpcClient and RpcClientT. Don't expose RpcClientT directly

* more doc tweaking about RpcParams and undo decision not to expose RpcParamsT

* Doc tweak

Co-authored-by: Alexandru Vasile <60601340+lexnv@users.noreply.github.com>

* more doc tweaks

* Fix doc thing

* Add an example of injecting a custom RPC client

* Fix a typo

* Address clippy things in example

* Fix a silly typo

* another clippy fix

* rpc_params to panic instead of returning a result, like serde_json::json, and deref on Rpc<T>

* fix docs

Co-authored-by: Alexandru Vasile <60601340+lexnv@users.noreply.github.com>

subxt/src/error.rs

@@ -15,7 +15,6 @@ pub use crate::metadata::{
     InvalidMetadataError,
     MetadataError,
 };
-pub use jsonrpsee::core::error::Error as RequestError;
 pub use scale_value::scale::{
     DecodeError,
     EncodeError,
@@ -36,7 +35,7 @@ pub enum Error {
     Codec(#[from] codec::Error),
     /// Rpc error.
     #[error("Rpc error: {0}")]
-    Rpc(#[from] RequestError),
+    Rpc(#[from] RpcError),
     /// Serde serialization error
     #[error("Serde json error: {0}")]
     Serialization(#[from] serde_json::error::Error),
@@ -102,6 +101,12 @@ impl From<DispatchError> for Error {
     }
 }
 
+/// An RPC error. Since we are generic over the RPC client that is used,
+/// the error is any custom string.
+#[derive(Debug, thiserror::Error)]
+#[error("RPC error: {0}")]
+pub struct RpcError(pub String);
+
 /// This is our attempt to decode a runtime DispatchError. We either
 /// successfully decode it into a [`ModuleError`], or we fail and keep
 /// hold of the bytes, which we can attempt to decode if we have an
@@ -232,7 +237,7 @@ pub enum TransactionError {
     /// block hasn't yet been finalized).
     #[error("The finality subscription expired")]
     FinalitySubscriptionTimeout,
-    /// The block hash that the tranaction was added to could not be found.
+    /// The block hash that the transaction was added to could not be found.
     /// This is probably because the block was retracted before being finalized.
     #[error("The block containing the transaction can no longer be found (perhaps it was on a non-finalized fork?)")]
     BlockHashNotFound,