This PR enhances the Wire library to support std::function–based callbacks for I2C slave mode, enabling the use of lambdas and captured contexts.
- Replaces raw function pointers in TwoWire and HardwareI2C with std::function for onRequest and onReceive
- Updates constructors, method signatures, and default initializations to use std::function
- Adds new example sketch, CI config, and documentation updates demonstrating the functional callback API
