Fix use of anchor/bundle opret/tapret dichotomies

[dr-orlovsky]

Due to use of two different DBC commitment schemes, tapret and opret, a witness transaction may contain two different DBC commitments, and, thus, anchors. Before v0.11.0-beta.6, there was a 1-to-(1,2)-to-(1,2) relation between witness transactions, anchors and state transition bundles. v0.11.0-beta.6 introduced that each bundle must be used just in a single anchor, and thus, has to commit to a specific DBC scheme. This PR completes implementation of this feature basing on test-driven approach from RGB-WG/rgb-tests#6

[codecov]

Codecov Report

Attention: Patch coverage is 1.14504% with 259 lines in your changes missing coverage. Please review.

Project coverage is 19.2%. Comparing base (670a7b6) to head (d1ee1d0).
Report is 38 commits behind head on master.

Files with missing lines	Patch %	Lines
src/containers/anchors.rs	2.2%	133 Missing ⚠️
src/persistence/stash.rs	0.0%	49 Missing ⚠️
src/containers/partials.rs	0.0%	32 Missing ⚠️
src/persistence/stock.rs	0.0%	20 Missing ⚠️
src/persistence/memory.rs	0.0%	10 Missing ⚠️
src/containers/indexed.rs	0.0%	9 Missing ⚠️
src/persistence/index.rs	0.0%	3 Missing ⚠️
src/persistence/state.rs	0.0%	2 Missing ⚠️
src/containers/consignment.rs	0.0%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           master    #277     +/-   ##
========================================
- Coverage    19.5%   19.2%   -0.3%     
========================================
  Files          40      39      -1     
  Lines        8453    8621    +168     
========================================
+ Hits         1652    1655      +3     
- Misses       6801    6966    +165     

Flag	Coverage Δ
rust	19.2% <1.1%> (-0.3%)	⬇️

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