refactor(share): IPLD/NMT improvements

[walldiss]

Closes https://github.com/celestiaorg/celestia-node/issues/183

[codecov-commenter]

Codecov Report

Merging #1223 (17c67e7) into main (738b69f) will increase coverage by 0.54%. The diff coverage is 66.66%.

@@            Coverage Diff             @@
##             main    #1223      +/-   ##
==========================================
+ Coverage   55.64%   56.19%   +0.54%     
==========================================
  Files         160      160              
  Lines        9862     9745     -117     
==========================================
- Hits         5488     5476      -12     
+ Misses       3838     3734     -104     
+ Partials      536      535       -1     

Impacted Files	Coverage Δ
share/ipld/namespace_hasher.go	100.00% <ø> (ø)
share/ipld/nmt.go	51.47% <55.17%> (+17.35%)	:arrow_up:
share/get.go	81.25% <100.00%> (-0.39%)	:arrow_down:
share/ipld/get.go	92.66% <100.00%> (+1.10%)	:arrow_up:
share/ipld/nmt_adder.go	79.48% <100.00%> (-0.52%)	:arrow_down:
das/coordinator.go	92.64% <0.00%> (+1.47%)	:arrow_up:
fraud/pb/proof.pb.go	36.61% <0.00%> (+1.89%)	:arrow_up:
fraud/bad_encoding.go	66.00% <0.00%> (+3.00%)	:arrow_up:
... and 1 more

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[Wondertan]

@walldiss, please also double check all the comments next change code, so we didn't miss anything and rebase