Thread safe piecereader

[aarshkshah1992]

Piecereader in it's current form is NOT thread-safe and we need concurrent access for Bitswap support.

[codecov]

Codecov Report

Merging #8397 (d0af0ef) into master (d502eeb) will decrease coverage by 0.05%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #8397      +/-   ##
==========================================
- Coverage   40.62%   40.57%   -0.06%     
==========================================
  Files         686      686              
  Lines       75333    75343      +10     
==========================================
- Hits        30607    30569      -38     
- Misses      39421    39465      +44     
- Partials     5305     5309       +4     

Impacted Files	Coverage Δ
extern/sector-storage/piece_reader.go	63.33% <100.00%> (+4.58%)	⬆️
chain/actors/builtin/miner/diff.go	48.52% <0.00%> (-10.30%)	⬇️
extern/sector-storage/faults.go	62.26% <0.00%> (-7.55%)	⬇️
chain/stmgr/searchwait.go	67.30% <0.00%> (-3.85%)	⬇️
node/hello/hello.go	63.63% <0.00%> (-3.41%)	⬇️
chain/stmgr/call.go	65.94% <0.00%> (-3.25%)	⬇️
chain/events/events_called.go	83.90% <0.00%> (-2.44%)	⬇️
extern/sector-storage/stores/index_locks.go	71.42% <0.00%> (-2.39%)	⬇️
miner/miner.go	56.39% <0.00%> (-1.97%)	⬇️
extern/storage-sealing/currentdealinfo.go	71.17% <0.00%> (-1.81%)	⬇️
... and 15 more