[WIP] Fix use of input model_path in the engine

[theocayla]

• Fix the use of model_path as input to instantiate the Engine
• Add checks on the model_path and onnx load

[codecov]

Codecov Report

Attention: Patch coverage is 27.27273% with 8 lines in your changes missing coverage. Please review.

Project coverage is 88.08%. Comparing base (5beb84c) to head (9c5b677).

Files with missing lines	Patch %	Lines
pyroengine/vision.py	27.27%	8 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #244      +/-   ##
===========================================
- Coverage    89.15%   88.08%   -1.07%     
===========================================
  Files            6        6              
  Lines          627      638      +11     
===========================================
+ Hits           559      562       +3     
- Misses          68       76       +8     

Flag	Coverage Δ
unittests	88.08% <27.27%> (-1.07%)	⬇️

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