Add enable/disable EOC interrupt functions for ADCs

[Tnze]

This patch allow user enable End of Convert interrupt for ADCs by calling adc1.enable_eoc_interrupt().

Tested on STM32F103CBT6, after enabling the eocie register. The interrupt ADC1_2 is triggered every time ADC convert is finished. This allows more efficient waiting for ADC result.

[Tnze]

@burrbull To make this useful. Addition changes are required.

We need a way taking apart convert() logic, and this is my temporary solution:
Tnze@6da9c4f

There is obvious problem of this and it will be good to have someone to design a better API.

[Tnze]

I just realized that read() function returns nb::Result which is the API needed here. Make it returns WouldBlock when the ADC convert not finished. But it will changes the behavior and all previous users need to wrap read() calls with nb::block!() to match the previous behavior.