Show prepared tasks in sealing jobs

[magik6k]

Currently tasks which are between the preparing and running states will disappear from lotus-miner sealing jobs output. This PR fixes that

TODO:

• Test that it actually works
• Fix prepared work starting too early

[codecov]

Codecov Report

Merging #7527 (e508055) into master (98ff1c4) will decrease coverage by 0.08%.
The diff coverage is 67.44%.

@@            Coverage Diff             @@
##           master    #7527      +/-   ##
==========================================
- Coverage   39.96%   39.88%   -0.09%     
==========================================
  Files         632      632              
  Lines       66926    66970      +44     
==========================================
- Hits        26750    26713      -37     
- Misses      35560    35633      +73     
- Partials     4616     4624       +8     

Impacted Files	Coverage Δ
cmd/lotus-miner/sealing.go	41.52% <0.00%> (-0.50%)	⬇️
extern/sector-storage/storiface/worker.go	53.84% <ø> (ø)
extern/sector-storage/stats.go	58.06% <33.33%> (-2.29%)	⬇️
extern/sector-storage/worker_tracked.go	76.53% <65.57%> (-13.62%)	⬇️
extern/sector-storage/sched.go	83.95% <100.00%> (-0.77%)	⬇️
extern/sector-storage/sched_worker.go	79.65% <100.00%> (+1.20%)	⬆️
chain/events/message_cache.go	87.50% <0.00%> (-12.50%)	⬇️
markets/loggers/loggers.go	89.28% <0.00%> (-10.72%)	⬇️
chain/actors/builtin/miner/diff.go	48.52% <0.00%> (-10.30%)	⬇️
chain/stmgr/call.go	67.87% <0.00%> (-7.28%)	⬇️
... and 18 more

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