Added test commands in contributing

[fe51]

This small PR updates the CONTRIBUTING test section

• by specifying the command to run end-to-end tests in order to git with CI workflows.
• updates commands for running specific pytests

Happy to discuss it :)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.07%. Comparing base (9cba4af) to head (11309b7).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #532   +/-   ##
=======================================
  Coverage   84.07%   84.07%           
=======================================
  Files          39       39           
  Lines        1212     1212           
=======================================
  Hits         1019     1019           
  Misses        193      193           

Flag	Coverage Δ
backend	83.40% <ø> (ø)
client	93.67% <ø> (ø)

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