Always add opret anchors when preset to a consignment

[dr-orlovsky]

Closes #271

I believe it should fix RGB-WG/rgb-tests#6

[codecov]

Codecov Report

Attention: Patch coverage is 0.79365% with 125 lines in your changes missing coverage. Please review.

Project coverage is 19.5%. Comparing base (94aeb57) to head (fc20101).
Report is 4 commits behind head on master.

Files with missing lines	Patch %	Lines
src/persistence/stock.rs	0.0%	32 Missing ⚠️
src/persistence/memory.rs	0.0%	30 Missing ⚠️
src/persistence/state.rs	0.0%	21 Missing ⚠️
src/persistence/stash.rs	0.0%	17 Missing ⚠️
src/containers/indexed.rs	0.0%	12 Missing ⚠️
src/containers/consignment.rs	12.5%	7 Missing ⚠️
src/containers/anchors.rs	0.0%	4 Missing ⚠️
src/persistence/index.rs	0.0%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           master    #272     +/-   ##
========================================
+ Coverage    19.2%   19.5%   +0.3%     
========================================
  Files          40      40             
  Lines        8603    8453    -150     
========================================
- Hits         1654    1652      -2     
+ Misses       6949    6801    -148     

Flag	Coverage Δ
rust	19.5% <0.8%> (+0.3%)	⬆️

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[zoedberg]

I've run the test in RGB-WG/rgb-tests#6 100 times and can confirm the test passed every time, so with this PR there is no more a non-deterministic behavior and transfers spending both tapret and opret allocations work again.