ManagedBlockChain: Use serialization framework for responses

[bblommers]

Not all of the methods were tested correctly, so this PR also adds a bunch of assertions to verify that the response is (still) correct.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.02%. Comparing base (d477e71) to head (3890ded).
⚠️ Report is 11 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #9428      +/-   ##
==========================================
- Coverage   93.02%   93.02%   -0.01%     
==========================================
  Files        1292     1292              
  Lines      116081   116062      -19     
==========================================
- Hits       107981   107962      -19     
  Misses       8100     8100              

Flag	Coverage Δ
servertests	28.86% <0.00%> (+<0.01%)	⬆️
unittests	92.99% <100.00%> (-0.01%)	⬇️

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