Use a single map for methods (#362)

* Use a single map for methods

* fmt

* cargo fmt screwed indents somehow

* Use Arc instead of Box for async methods

* fmt

* Implement `execute` on `MethodCallback` to keep things DRY

* fmt

* `OwnedJsonRpcRequest` is not necessary anymore

* Call `execute` on `Methods` directly for even more DRY code

* Update utils/src/server/rpc_module.rs

Co-authored-by: Niklas Adolfsson <[email protected]>

* Use `copied` instead of mapping a deref

* DRY-er `params` in `MethodCallback`

* Added comment on `0` conn_id in http

Co-authored-by: Niklas Adolfsson <[email protected]>