feat(lib/blocktree): Prune returns ordered pruned forks

[qdm12]

Changes

The blocktree Prune method returns a mapping from fork origin block hash (part of the canonical chain) to an ordered slice of block hashes forming the now-dropped forked chain of blocks.

This allows the pruner to be 'fork-aware' and to find which deltas can be deleted safely from each fork, on finalisation. For example if a dropped fork chain inserted database key XYZ, we should remove it BUT we need to ensure this same key was not inserted by a block on the canonical chain as well. To do this, we need all the dropped forks ordered to work with their deltas and compare them with the canonical chain.

Tests

go test -tags integration github.com/ChainSafe/gossamer/lib/blocktree

Issues

Needed for PR #2831

Primary Reviewer

@timwu20

[codecov]

Codecov Report

Merging #3050 (54ae58f) into development (a179855) will increase coverage by 0.05%.
The diff coverage is 82.75%.

Additional details and impacted files

@@               Coverage Diff               @@
##           development    #3050      +/-   ##
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+ Coverage        51.01%   51.06%   +0.05%     
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  Files              224      224              
  Lines            28103    28127      +24     
===============================================
+ Hits             14336    14364      +28     
+ Misses           12385    12380       -5     
- Partials          1382     1383       +1     

[timwu20]

@qdm12 is this still required given we're removing the online pruner?

[qdm12]

@qdm12 is this still required given we're removing the online pruner?

Yes it's required for #2831 - I can bundle it in #2831 if you prefer though.