Use "guard list" for deliver()

[ponyisi]

By default, let deliver() return all requests made, even if some of them throw exceptions. Each return list is wrapped in a GuardList which will reraise any exception if the user attempts to access the corresponding result, and whose validity can be checked with .valid().

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 80.59%. Comparing base (f4b9e55) to head (1a4538f).

Additional details and impacted files

@@               Coverage Diff               @@
##           3.0_develop     #413      +/-   ##
===============================================
+ Coverage        79.75%   80.59%   +0.84%     
===============================================
  Files               26       26              
  Lines             1314     1340      +26     
===============================================
+ Hits              1048     1080      +32     
+ Misses             266      260       -6     

Flag	Coverage Δ
unittests	80.59% <100.00%> (+0.84%)	⬆️

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