Improve performance of ADC reads

[EarthenSky]

Building on #423

Performance is improved by 19 times, from 105ms per 8 ADC reads, to 5.5ms per 8 ADC reads.

It's possible to improve the performance more than 160 hz for all 8 ADC, however 1/3 of all time is being spend sleeping, while another 1/3 is spent transferring data over SPI. It's unlikely to get faster than 200 hz. The speed improvements are due to bit optimizations, minimizing data sent over the channel, python optimizations, and batching of requests (minimize system calls opening & closing devices), all of which were found via profiling. For more info, see this (private) page in the wiki.

Main Changes

• add batch_read_samples_adc1 with minimal calling of slow functions (get_state() is the evilest)
• refactor adc_commands functions to be static
• add read_command_tuple and spi_apply_adc_commands to efficiently read commands
• misc refactoring to minimize complexity where worthwhile

TODOs

• [x] test that updates to the EdgePiADC.__state are being applied correctly
• [x] make sure that unit & integration tests are sufficient

[EarthenSky]

Trace of 1 ADC read (before):

Trace of 8 ADC reads (optimized):

[github-actions[bot]]

Package	Line Rate	Branch Rate	Health
adc	92%	87%	✔
calibration	100%	100%	✔
dac	100%	97%	✔
digital_input	100%	91%	✔
digital_output	98%	95%	✔
eeprom	83%	63%	✔
eeprom.protobuf_assets.eeprom_data_classes	97%	52%	✔
eeprom.protobuf_assets.generated_pb2	77%	50%	✔
gpio	98%	94%	✔
led	0%	0%	❌
peripherals	69%	23%	➖
pwm	96%	95%	✔
reg_helper	97%	85%	✔
relay	100%	100%	✔
tc	98%	98%	✔
utilities	100%	100%	✔
Summary	92% (3176 / 3457)	80% (680 / 845)	✔