fix: vm: support raw blocks in chain export

[Stebalien]

Related Issues

Proposed Changes

Support raw blocks in chain export. We now visit them, we just don't recurs on them.

We need this for NV16 to include code in chain snapshots.

NOTE: I've also checked the splitstore, and we appear to be doing the right thing there already.

Checklist

Before you mark the PR ready for review, please make sure that:

• All commits have a clear commit message.
• The PR title is in the form of of <PR type>: <area>: <change being made>
  • example: fix: mempool: Introduce a cache for valid signatures
  • PR type: fix, feat, INTERFACE BREAKING CHANGE, CONSENSUS BREAKING, build, chore, ci, docs,perf, refactor, revert, style, test
  • area: api, chain, state, vm, data transfer, market, mempool, message, block production, multisig, networking, paychan, proving, sealing, wallet, deps
• This PR has tests for new functionality or change in behaviour
• If new user-facing features are introduced, clear usage guidelines and / or documentation updates should be included in https://lotus.filecoin.io or Discussion Tutorials.
• CI is green

[codecov]

Codecov Report

Merging #8691 (f491e39) into master (8552cdb) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #8691      +/-   ##
==========================================
+ Coverage   40.85%   40.88%   +0.02%     
==========================================
  Files         687      687              
  Lines       75840    75845       +5     
==========================================
+ Hits        30987    31007      +20     
+ Misses      39517    39491      -26     
- Partials     5336     5347      +11     

Impacted Files	Coverage Δ
chain/store/snapshot.go	66.66% <100.00%> (+1.61%)	⬆️
chain/events/observer.go	73.79% <0.00%> (-6.21%)	⬇️
storage/wdpost_sched.go	75.49% <0.00%> (-5.89%)	⬇️
extern/storage-sealing/currentdealinfo.go	70.17% <0.00%> (-5.27%)	⬇️
chain/events/events_called.go	83.90% <0.00%> (-4.40%)	⬇️
chain/sub/incoming.go	59.02% <0.00%> (-2.45%)	⬇️
storage/wdpost_changehandler.go	97.64% <0.00%> (-0.95%)	⬇️
chain/gen/gen.go	68.80% <0.00%> (-0.62%)	⬇️
chain/store/store.go	64.83% <0.00%> (-0.50%)	⬇️
storage/wdpost_run.go	70.48% <0.00%> (-0.39%)	⬇️
... and 14 more

[vyzo]

we need to cherry pick this for the nv16 branch.