Support retrieval UnsealPrice (#325)

[ingar]

Summary

Add states and logic to support setting of and paying for unsealing of data.

Resolves #325

[codecov-commenter]

Codecov Report

Merging #330 into master will decrease coverage by 0.34%.
The diff coverage is 50.00%.

@@            Coverage Diff             @@
##           master     #330      +/-   ##
==========================================
- Coverage   63.09%   62.75%   -0.33%     
==========================================
  Files          40       40              
  Lines        2419     2451      +32     
==========================================
+ Hits         1526     1538      +12     
- Misses        787      803      +16     
- Partials      106      110       +4     

Impacted Files	Coverage Δ
retrievalmarket/impl/dtutils/dtutils.go	74.25% <0.00%> (-2.32%)	⬇️
...etrievalmarket/impl/providerstates/provider_fsm.go	10.00% <ø> (ø)
...ievalmarket/impl/providerstates/provider_states.go	88.10% <0.00%> (-11.90%)	⬇️
...market/impl/requestvalidation/requestvalidation.go	85.97% <20.00%> (-6.76%)	⬇️
retrievalmarket/impl/clientstates/client_fsm.go	76.54% <42.86%> (-2.81%)	⬇️
retrievalmarket/types.go	45.10% <42.86%> (-0.55%)	⬇️
retrievalmarket/impl/provider_environments.go	71.43% <60.00%> (-1.45%)	⬇️
retrievalmarket/impl/client.go	71.78% <100.00%> (+0.23%)	⬆️
retrievalmarket/impl/clientstates/client_states.go	94.37% <100.00%> (+0.34%)	⬆️
retrievalmarket/impl/provider.go	76.53% <100.00%> (+1.97%)	⬆️
... and 3 more

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[hannahhoward]

LGTM

[hannahhoward]

LGTM