Refactor AT24Cxx I2C interface and add I2c helper

Modernize AT24Cxx EEPROM driver and underlying I2C API: rename constants to k-prefixed identifiers, update copyright year, replace direct HAL FUNC_PREFIX I2C calls with i2c:: wrapper calls, and simplify member names and signatures. Add an I2c helper class to lib-gd32/include/i2c.h encapsulating common read/write/ack/setup operations and include optional GCC optimize push/pop pragmas for i2c and spi headers. Also adjust AT24Cxx template internals for clearer naming, page/address logic, and provide explicit constructors for AT24C04/AT24C32.

Author: vanvught