VREF-olutionary: VREF support/instantiation for ADCs

[oleglazari]

Add configurable VREF voltage support to the ADC system for improved measurement accuracy.

The ADC bases its voltage calculations from the VREF pin on the STM32F302R8, but the ADC hardware doesn't implicitly know what the actual voltage at VREF is. Previously, the system assumed a hardcoded 3.3V reference, which could lead to inaccurate voltage readings when using different reference voltages.

This PR adds setVref(float vref) and getVref() methods to the ADC interface, enabling accurate measurements with various reference voltages (1.8V, 3.3V, 5.0V, etc.). The implementation replaces hardcoded VREF values with configurable runtime settings in both STM32F3xx and F4xx platforms.

io::ADC& adc = io::getADC<io::Pin::PA_0, io::ADCPeriph::ONE>();
adc.setVref(5.0f);  // Set 5V reference
float voltage = adc.read();  // Now calculated with correct VREF

And do not fret, the default will always be 3.3V so old ADC code will not break

[ActuallyTaylor]

Looks mostly good! I just see a quick code removal in one of the samples.

[EvanHughes-dev]

Overall it looks good. There's just two comments (really the same comment) that needs clarification.

[mjh9585]

Two small comments.

[EvanHughes-dev]

LGTM