Remove exported error codes from the MCP package #535
Description
For likely historical reasons, we exposed JSON-RPC error codes in the MCP package: CodeResourceNotFound, CodeUnsupportedMethod, CodeInvalidParams.
These can't be useful yet, as we haven't exposed jsonrpc.Error (see #452) (there is no way to get or set them in an error).
They are also arbitrary.
I consider it a bug that they are exposed. We should remove them, add jsonrpc.Error, and only add them back if requested. They might be more appropriate in the jsonrpc package.
CC @jba