Execute a generic RPC method on a call. This is the low-level interface for
cross-call communication. For common operations, prefer the specific helpers
rpcDial(),
rpcAiMessage(), and
rpcAiUnhold().
RPC configuration object.
RPC method name (e.g., "dial", "ai_message", "ai_unhold").
Parameters for the RPC method.
Target call ID for the RPC command.
Target node ID for the RPC command.
FunctionResult — this, for chaining.