Clean some TODOs and harmonize unit tests

[zguesmi]

• // TODO: Remove header bellow
• // TODO use IexecOrders.toArray() for spreading and remove type Orders
• Replace some async function () by async () =>
• Remove dynamic string keys from IexecOrders for better compilation and use @ts-ignore when needed.
• // TODO remove these additional return values and use function toObject() for deserialization
• Add some missing .then((tx) => tx.wait()) in Boost unit tests.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.02%. Comparing base (cf15dc0) to head (f3791f7).
Report is 13 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #123   +/-   ##
========================================
  Coverage    84.02%   84.02%           
========================================
  Files           35       35           
  Lines         1077     1077           
  Branches       201      221   +20     
========================================
  Hits           905      905           
  Misses         172      172           

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[james-toussaint]

Thanks!