feat: Reject promise immediately if var not found

[wusteven815]

• Implements Reject promise immediately if variable is not in first message of field updates #1701
• fetchVariableDefinition now throws an Error when a variable is not found (instead of throwing TimeoutError)
• TimeoutError still used and will be thrown on an actual timeout
• Tests added to check for the correct error

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (73e1837) 46.44% compared to head (1a2626a) 46.44%.
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1718   +/-   ##
=======================================
  Coverage   46.44%   46.44%           
=======================================
  Files         611      611           
  Lines       37204    37206    +2     
  Branches     9363     9364    +1     
=======================================
+ Hits        17279    17281    +2     
  Misses      19871    19871           
  Partials       54       54           

Flag	Coverage Δ
unit	46.44% <100.00%> (+<0.01%)	⬆️

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[mofojed]

Looks good! Just a minor correction to the error message.