Add support for setting encoder position

[caternuson]

For #20. Implements setting encoder position.

Tested with a PID 5752 and QT PY RP2040 running CP.

BEFORE

Adafruit CircuitPython 8.2.2 on 2023-07-31; Adafruit QT Py RP2040 with rp2040
>>> import board
>>> from adafruit_seesaw.seesaw import Seesaw
>>> i2c = board.STEMMA_I2C()
>>> ss = Seesaw(i2c, addr=73)
>>> for i in range(4):
...     print(ss.encoder_position(i))
... 
-11
-11
8
10
>>> for i in range(4):
...     ss.set_encoder_position(2342, i)
... 
>>> for i in range(4):
...     print(ss.encoder_position(i))
... 
-11
-11
8
10
>>>

AFTER

Adafruit CircuitPython 8.2.2 on 2023-07-31; Adafruit QT Py RP2040 with rp2040
>>> import board
>>> from adafruit_seesaw.seesaw import Seesaw
>>> i2c = board.STEMMA_I2C()
>>> ss = Seesaw(i2c, addr=73)
>>> for i in range(4):
...     print(ss.encoder_position(i))
... 
5
-7
1
15
>>> for i in range(4):
...     ss.set_encoder_position(2342, i)
... 
>>> for i in range(4):
...     print(ss.encoder_position(i))
... 
2342
2342
2342
2342
>>>

[caternuson]

@ladyada for review

[jmeier5261]

I was extremely disappointed that this functionality was not in the stock firmware since its a core function of rotary encoders. Thankfully I was able to find this PR through the forums and after $10 and a few days waiting I had the programmer. I was able to flash this on my 5752 Quad encoder board using the ATtiny817 and confirmed the functionality using my Arduino Nano ESP32 board and Arduino IDE (After messing with the seesaw library a little to get it to compile for the nano esp32). I would suggest merging this and making it the default firmware on these boards moving forward since its not reasonable to expect everyone to flash it manually just to get some basic functionality working especially since the programmer is needed and the megaTinyCore board package doesn't work for Arduino IDE 2.X. Cheers for the PR and thank you for your work