Refactor and modify OutOfBandReceiver

[Patrik-Stas]

• Refactoring
• Modified behaviour - do not modify decorators on retrieved attached message - I don't know why this was being done in a first place (perhaps trying to be graceful toward misbehaving OOB sender message?)

[codecov-commenter]

Codecov Report

Merging #1038 (8997e88) into main (2229bab) will increase coverage by 0.00%.
The diff coverage is 0.00%.

@@          Coverage Diff          @@
##            main   #1038   +/-   ##
=====================================
  Coverage   0.05%   0.05%           
=====================================
  Files        383     383           
  Lines      21288   21254   -34     
  Branches    3837    3830    -7     
=====================================
  Hits          12      12           
+ Misses     21275   21241   -34     
  Partials       1       1           

Flag	Coverage Δ
unittests-aries-vcx	0.05% <0.00%> (+<0.01%)	⬆️

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Files	Coverage Δ
aries_vcx/src/handlers/out_of_band/receiver.rs	0.00% <0.00%> (ø)