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 83.27%. Comparing base (29bb3ff) to head (8a154d9).
Report is 4 commits behind head on master.

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%   83.27%   -0.06%     
==========================================
  Files         334      334              
  Lines       46445    46446       +1     
==========================================
- Hits        38704    38680      -24     
- Misses       6163     6192      +29     
+ Partials     1578     1574       -4     

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