Function private_rpc_version 

pub const fn private_rpc_version(
    api_key: i16,
    krabka_version: i16,
) -> Option<i16>

The highest request version of the private controller RPC api_key that a node may send when the finalized krabka.version is krabka_version.

Returns None for an api key that is not a private controller RPC, and for a level this build does not support. At levels 0 to 3 every RPC is v0.