Parallelize validate

[ssssarah]

• the traverse function being optionally overwritten on Shape was due to a change in pyshacl versions (I believe an old version had this version but a newer one no longer had it. For the version we have fixed, this function does not exist) Install required version of Pyshacl when installing Nexus Forge #43 Fix temporary the Shape.traverse() issue #44
• renamed usage of _transitive_load_shape_graph to _transitive_load_resource_graph
• dummy implementation of _validate_many in DemoModel
• Override pyshacl ShapesGraph implementation of def shapes to return list instead of dict_values() so that it can be picklable (for multiprocessing)
• Parallelized validate.
  -> cannot use threads because pyshacl uses rdflib, rdflib uses pyparsing and it is not thread safe
  -> shape loading occurs before creating multiple processes for validation. It would be possible to load shapes in individual processes, however:
  - "caching" of shapes becomes useless, the same shape will be queried multiple times across processes
  - Shape loading in individual processes would be best if validating resources of different types/shapes
  - The former point might not be completely true because shapes re-use each other
  - It is for sure better to load the shapes beforehand if we're dealing with a list of resources of the same type/shape.
  Given these reasons, I opted for loading all shapes beforehand.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 95.06173% with 4 lines in your changes missing coverage. Please review.

Project coverage is 74.19%. Comparing base (a1ae462) to head (19e3556).

Files	Patch %	Lines
kgforge/specializations/models/rdf/service.py	95.34%	2 Missing ⚠️
...gforge/specializations/models/rdf/store_service.py	0.00%	1 Missing ⚠️
kgforge/specializations/models/rdf_model.py	97.22%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #418      +/-   ##
==========================================
+ Coverage   74.13%   74.19%   +0.05%     
==========================================
  Files         106      106              
  Lines        6979     6998      +19     
==========================================
+ Hits         5174     5192      +18     
- Misses       1805     1806       +1     

Flag	Coverage Δ
unittests	74.19% <95.06%> (+0.05%)	⬆️

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[ssssarah]

Unfortunately I ran into an issue when testing validation on 4000 resources.
Long story short, pyshacl uses rdflib, rdflib uses pyparsing and it is not thread safe
RDFLib/rdflib#765 I'll look more into it