* Use rp2040-hal in all example (possibly through their bsp)
Some of the examples were using the cortex_m_rt::entry method which
misses the device specific spinlock re-initialisation.
This commits makes the usage more consistent by using rp2040_hal exported
macro as the only `entry` method used across examples.
* Add struct VectorTable to represent an interrupt vector table
* Add member function to VectorTable to initialise based on the current Interrupt Vector Table from VTOR
* Add member function to VectorTable to register an extern "C" function to call on interrupt
* Add example using VectorTable to demonstrate initialisation and interrupt function registration
