//! Special Function Codes Module
//!
//! This module is reserved for special purposes. If an organization has
//! proprietary or custom function codes that are not part of the standard
//! Modbus Public Function Codes, those will be declared and managed here.
//!
//! This allows the library to be extended for vendor-specific implementations
//! while keeping the core public function codes compliant with the
//! Modbus Application Protocol Specification.
