- don't require an irq binding for blocking-only adc
- abstract adc pins into an AnyPin like interface, erasing the actual
peripheral type at runtime.
- add pull-up/pull-down functions for adc pins
- add a test (mostly a copy of the example, to be honest)
- configure adc pads according to datasheet
- report conversion errors (although they seem exceedingly rare?)
- drop embedded-hal interfaces. embedded-hal channels can do neither
AnyPin nor pullup/pulldown without encoding both into the type
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