Add support for 3- and 4-tuples in `@@deriving rpcty` & fix Python exceptions
- rpclib:
- New
Rpc.Types
variants for 3- and 4-tuples - pythongen: fix generated exceptions
- Remove broken
Rpc_client
- New
- ppx_deriving_rpc:
- rpcty ppx: Add support for 3- and 4-tuples