Replace APISchema Serialization with Pydantic 1.0

[DiamondJoseph]

Closes #125

• Use Pydantic Dataclasses for types that will be serialised/deserialised only (i.e., ComponentConfigs)
• Remove tests that check APISchema specific behaviour
• Refactor example configs to use discriminator field handling and more explicit handling of ComponentPort

[codecov]

Codecov Report

Merging #154 (38e6e8a) into master (17255c6) will decrease coverage by 0.48%.
The diff coverage is 90.54%.

@@            Coverage Diff             @@
##           master     #154      +/-   ##
==========================================
- Coverage   94.97%   94.50%   -0.48%     
==========================================
  Files          44       44              
  Lines        1294     1292       -2     
==========================================
- Hits         1229     1221       -8     
- Misses         65       71       +6     

Impacted Files	Coverage Δ
src/tickit/core/adapter.py	91.66% <ø> (-1.20%)	⬇️
src/tickit/core/device.py	100.00% <ø> (ø)
src/tickit/core/typedefs.py	97.50% <ø> (+1.58%)	⬆️
src/tickit/utils/configuration/tagged_union.py	87.23% <87.23%> (ø)
src/tickit/utils/byte_format.py	91.66% <91.66%> (-8.34%)	⬇️
src/tickit/core/components/component.py	96.29% <100.00%> (ø)
src/tickit/core/components/system_simulation.py	97.77% <100.00%> (ø)
src/tickit/devices/iobox.py	97.29% <100.00%> (+0.15%)	⬆️
src/tickit/devices/sink.py	100.00% <100.00%> (ø)
src/tickit/devices/source.py	100.00% <100.00%> (ø)
... and 1 more