testing: tool to dump blocks to directory

[cce]

Summary

This adds a small program that helps you write out a range or random set of blocks from a provided SQLite blockdb to a directory.

[codecov]

Codecov Report

Merging #4595 (738b6dd) into master (42b9533) will increase coverage by 0.02%.
The diff coverage is 87.50%.

@@            Coverage Diff             @@
##           master    #4595      +/-   ##
==========================================
+ Coverage   54.10%   54.12%   +0.02%     
==========================================
  Files         401      401              
  Lines       51642    51649       +7     
==========================================
+ Hits        27942    27957      +15     
+ Misses      21345    21338       -7     
+ Partials     2355     2354       -1     

Impacted Files	Coverage Δ
agreement/proposal.go	71.96% <ø> (ø)
agreement/actions.go	71.42% <50.00%> (-0.20%)	⬇️
agreement/demux.go	90.68% <100.00%> (+0.13%)	⬆️
agreement/events.go	61.62% <100.00%> (+0.45%)	⬆️
ledger/blockqueue.go	85.63% <0.00%> (-2.88%)	⬇️
ledger/tracker.go	74.04% <0.00%> (-0.86%)	⬇️
network/wsNetwork.go	64.63% <0.00%> (ø)
catchup/service.go	69.38% <0.00%> (+0.74%)	⬆️
cmd/tealdbg/debugger.go	73.49% <0.00%> (+0.80%)	⬆️
network/wsPeer.go	68.19% <0.00%> (+2.15%)	⬆️
... and 1 more

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