use class method for processors

[magland]

@luiztauffer

Here I have implemented the new class method for protocaas processors.

You can see the examples here:
https://github.com/scratchrealm/pc-spike-sorting/blob/main/mountainsort5/main.py
https://github.com/scratchrealm/pc-spike-sorting/blob/main/kilosort3/main.py
https://github.com/scratchrealm/pc-spike-sorting/blob/main/kilosort2_5/main.py
https://github.com/scratchrealm/pc-spike-sorting/blob/main/dandi_upload/main.py
https://github.com/scratchrealm/pc-spike-sorting/blob/main/spike_sorting_utils/main.py

The tricky part was getting the meta information about the processor context from the type hints, etc. That is done here:

https://github.com/scratchrealm/protocaas/blob/1a5134ebbc1e8673c2de44a3b32740e28ddbb024/python/protocaas/sdk/AppProcessor.py#L169-L268
https://github.com/scratchrealm/protocaas/blob/1a5134ebbc1e8673c2de44a3b32740e28ddbb024/python/protocaas/sdk/_get_context_attributes_for_dataclass.py#L1-L32

Unfortunately, inspecting of type hints did not work with your method of dynamically importing the main.py module, so I had to revert to calling main.py with the SPEC_OUTPUT_FILE env var. However, the CLI works the same as you had it, for example

protocaas make-app-spec-file --app-dir kilosort3 --spec-output-file kilosort3/spec.json

(also, sprinkled into this PR, are some improvements/simplifications to the mock system for testing)

[codecov]

Codecov Report

Attention: 110 lines in your changes are missing coverage. Please review.

Files	Coverage Δ
...n/protocaas/api_helpers/clients/MockMongoClient.py	84.52% <100.00%> (+0.37%)	⬆️
...protocaas/api_helpers/clients/_get_mongo_client.py	81.48% <100.00%> (+4.20%)	⬆️
python/protocaas/api_helpers/clients/pubsub.py	43.47% <100.00%> (-6.53%)	⬇️
...aas/api_helpers/routers/compute_resource/router.py	76.13% <100.00%> (-0.54%)	⬇️
python/protocaas/mock.py	100.00% <100.00%> (ø)
python/protocaas/sdk/__init__.py	100.00% <100.00%> (ø)
...api_helpers/routers/gui/compute_resource_routes.py	46.71% <50.00%> (-0.70%)	⬇️
python/protocaas/sdk/ProcessorBase.py	68.42% <68.42%> (ø)
python/protocaas/sdk/_make_spec_file.py	0.00% <0.00%> (ø)
...ocaas/sdk/_get_context_attributes_for_dataclass.py	45.45% <45.45%> (ø)
... and 2 more

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