fix: dot/network: improve syncing at head

[noot]

Changes

• allow syncer to allow block requests of variable size and start value when "near" the head (ie. node head block is less than 128 blocks away from chain head)
• update blocktree.AddBlock to accept types.Header (since it doesn't need the block body)
• remove highestBlockHeader from BlockState since it's unused
• update syncer to allow syncing blocks with number below our head (needed in case of chain forks, small ones are likely near the head)
• handle BlockData processing failure better by requesting parent block if we have a "failed to get parent hash" error (this seems to happen near the head often)

Tests

go test ./dot/network -short
go test ./dot/sync -short
go test ./lib/blocktree

Issues

• closes Sync Kusama Network #1134
• closes Interop with Kusama #580

[codecov]

Codecov Report

Merging #1465 (605a42e) into development (34befe0) will increase coverage by 0.19%.
The diff coverage is 52.40%.

@@               Coverage Diff               @@
##           development    #1465      +/-   ##
===============================================
+ Coverage        57.82%   58.01%   +0.19%     
===============================================
  Files              152      152              
  Lines            15226    15307      +81     
===============================================
+ Hits              8804     8881      +77     
+ Misses            4878     4871       -7     
- Partials          1544     1555      +11     

Flag	Coverage Δ
unit-tests	58.01% <52.40%> (+0.19%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
dot/config.go	34.64% <0.00%> (ø)
dot/core/test_helpers.go	74.03% <0.00%> (ø)
lib/utils/utils.go	24.35% <0.00%> (ø)
dot/state/block.go	47.12% <16.66%> (-0.94%)	⬇️
dot/sync/syncer.go	42.78% <40.47%> (-2.09%)	⬇️
dot/network/sync.go	63.70% <65.03%> (+8.27%)	⬆️
cmd/gossamer/config.go	73.10% <100.00%> (-0.14%)	⬇️
dot/network/test_helpers.go	75.80% <100.00%> (+1.61%)	⬆️
dot/state/storage.go	41.80% <100.00%> (+1.12%)	⬆️
dot/sync/message.go	68.75% <100.00%> (ø)
... and 6 more

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[edwardmack]

This looks great, it closes an Epic, that's epic! Also, nice idea moving the logger out of the struct.