Update to new data transfer

[hannahhoward]

Goals

Update data transfer to the new version

Implementation

For now, just a few changes to storage market to make things work --

• setting up the subscriber to look for completion state rather than events
• created a test channel struct that will be useful for retrieval
• initialization code for integrations tests
• validators return nil voucher results for now

[codecov-commenter]

Codecov Report

Merging #317 into master will decrease coverage by 0.24%.
The diff coverage is 60.00%.

@@            Coverage Diff             @@
##           master     #317      +/-   ##
==========================================
- Coverage   63.85%   63.62%   -0.23%     
==========================================
  Files          41       41              
  Lines        2600     2608       +8     
==========================================
- Hits         1660     1659       -1     
- Misses        819      827       +8     
- Partials      121      122       +1     

Impacted Files	Coverage Δ
retrievalmarket/types.go	37.50% <0.00%> (-6.61%)	⬇️
storagemarket/impl/dtutils/dtutils.go	70.59% <66.67%> (ø)
...oragemarket/impl/providerstates/provider_states.go	87.81% <100.00%> (+0.13%)	⬆️
...mpl/requestvalidation/unified_request_validator.go	75.00% <100.00%> (ø)
retrievalmarket/impl/blockio/traverser.go	68.89% <0.00%> (-3.33%)	⬇️

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