fix: Show different error message for cancelled requests when Snap is stopped

[FrederikBolding]

Show a different error message for cancelled requests when the Snap is stopped. Right now, we show the generic "failed to respond in time" message, which is very confusing.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.24%. Comparing base (7a1340b) to head (fc55b9d).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3518   +/-   ##
=======================================
  Coverage   98.24%   98.24%           
=======================================
  Files         408      408           
  Lines       11517    11520    +3     
  Branches     1792     1795    +3     
=======================================
+ Hits        11315    11318    +3     
  Misses        202      202           

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