Switch from using apischema to pydantic

[callumforrester]

• Replace all public dataclasses with BaseModels.
• Add "type validators" to replicate device lookup behaviour. They do not work as well as apischema converters and various workarounds were needed. Will make issues off of this PR.
• Add tests

[codecov]

Codecov Report

Merging #90 (1cfbd0e) into main (8e754f3) will increase coverage by 1.42%.
The diff coverage is 84.41%.

@@            Coverage Diff             @@
##             main      #90      +/-   ##
==========================================
+ Coverage   72.13%   73.55%   +1.42%     
==========================================
  Files          35       36       +1     
  Lines         976     1040      +64     
==========================================
+ Hits          704      765      +61     
- Misses        272      275       +3     

Impacted Files	Coverage Δ
src/blueapi/cli/cli.py	60.71% <0.00%> (ø)
src/blueapi/core/__init__.py	100.00% <ø> (ø)
src/blueapi/service/app.py	40.35% <0.00%> (ø)
src/blueapi/worker/reworker.py	33.33% <0.00%> (ø)
src/blueapi/plans/plans.py	61.11% <50.00%> (-0.43%)	⬇️
src/blueapi/worker/task.py	72.41% <61.53%> (+2.64%)	⬆️
src/blueapi/core/context.py	78.12% <75.00%> (-2.65%)	⬇️
src/blueapi/service/model.py	80.64% <87.50%> (-4.36%)	⬇️
src/blueapi/utils/serialization.py	87.50% <87.50%> (ø)
src/blueapi/utils/type_validator.py	87.60% <87.60%> (ø)
... and 7 more

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