fix restarts during data transfer for a retrieval deal

[dirkmc]

Fixes #533
Supersedes #539
Depends on filecoin-project/go-data-transfer#197

TODO:

• Clean up logging & commented out code
• Handle case where transfer is restarted in validatePull()
• Manual test

[aarshkshah1992]

@dirkmc

First round of comments/questions.

[codecov-commenter]

Codecov Report

Merging #540 (25f4f77) into master (be1da4a) will increase coverage by 0.23%.
The diff coverage is 83.90%.

@@            Coverage Diff             @@
##           master     #540      +/-   ##
==========================================
+ Coverage   65.54%   65.77%   +0.23%     
==========================================
  Files          53       56       +3     
  Lines        3549     3634      +85     
==========================================
+ Hits         2326     2390      +64     
- Misses        990     1009      +19     
- Partials      233      235       +2     

Impacted Files	Coverage Δ
retrievalmarket/dealstatus.go	0.00% <0.00%> (ø)
retrievalmarket/events.go	0.00% <0.00%> (ø)
...etrievalmarket/impl/providerstates/provider_fsm.go	6.46% <0.00%> (ø)
...mpl/requestvalidation/unified_request_validator.go	81.82% <ø> (ø)
storagemarket/events.go	37.50% <37.50%> (ø)
retrievalmarket/impl/clientstates/client_fsm.go	68.60% <85.72%> (-4.05%)	⬇️
...rievalmarket/impl/requestvalidation/revalidator.go	76.97% <89.29%> (+1.80%)	⬆️
retrievalmarket/impl/clientstates/client_states.go	94.34% <100.00%> (+1.94%)	⬆️
retrievalmarket/impl/dtutils/dtutils.go	79.44% <100.00%> (ø)
retrievalmarket/impl/provider_environments.go	55.96% <100.00%> (+0.54%)	⬆️
... and 6 more

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[aarshkshah1992]

@dirkmc Have finished the review. Some questions/concerns.

Astounding work !

[aarshkshah1992]

Just one comment. LGTM.