blockfetcher: add more details to errors

[AliceInHunterland]

Close #3629

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.

Project coverage is 83.33%. Comparing base (29bb3ff) to head (bb4d628).

Files with missing lines	Patch %	Lines
pkg/services/blockfetcher/blockfetcher.go	0.00%	3 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3636   +/-   ##
=======================================
  Coverage   83.33%   83.33%           
=======================================
  Files         334      334           
  Lines       46445    46445           
=======================================
  Hits        38704    38704           
  Misses       6163     6163           
  Partials     1578     1578           

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