Function validate_read_write_registers 

pub fn validate_read_write_registers(
    read_address: u16,
    read_quantity: u16,
    write_address: u16,
    write_quantity: u16,
    write_byte_count: u8,
) -> Result<(), ExceptionCode>

Validate a read/write multiple registers (FC 17) request.

Per spec §6.17 Figure 27 state diagram.

Errors

• IllegalDataValue if quantities out of range or byte count doesn’t match
• IllegalDataAddress if either address+quantity overflows