Function private_api_highest_version 

pub const fn private_api_highest_version(api_key: i16) -> Option<i16>

The highest version of the krabka-private api_key this build serves, or None when api_key is not one of them.

It is the version the krabka.version table gives at this build’s KRABKA_VERSION_MAX. A receiver serves every version from 0 up to it, because a sender may send any version that a level up to that maximum gives, and a level never lowers a version.