RGB "decentralized geneses": contract unowned extensions & valencies implementation

[dr-orlovsky]

See LNP-BP/LNPBPs#52 for explanations. This PR implements:

• Schema for extensions
• Schema validation
• Extension implementation within RGB contracts
• Inclusion of extension data into consignments
• Consignments validation for extensions

@rajarshimaitra can you pls update test data to make tests not failing? And we need to add test coverage where it is missed.

[rajarshimaitra]

Noted, will work on the test updates.

[rajarshimaitra]

Yeah. Finally managed to push it.

[codecov]

Codecov Report

Merging #112 into master will decrease coverage by 0.4%.
The diff coverage is 39.0%.

@@           Coverage Diff            @@
##           master    #112     +/-   ##
========================================
- Coverage    57.9%   57.5%   -0.4%     
========================================
  Files          59      59             
  Lines        6581    6851    +270     
========================================
+ Hits         3810    3941    +131     
- Misses       2771    2910    +139     

Impacted Files	Coverage Δ
src/rgb/bech32.rs	0.0% <0.0%> (ø)
src/rgb/schema/script.rs	40.0% <0.0%> (-2.9%)	⬇️
src/rgb/stash/consignment.rs	0.0% <0.0%> (-52.8%)	⬇️
src/rgb/validation.rs	0.0% <0.0%> (-19.6%)	⬇️
src/rgb/schema/schema.rs	34.4% <36.1%> (+1.0%)	⬆️
src/rgb/schema/nodes.rs	84.7% <81.6%> (+6.0%)	⬆️
src/lnpbps/lnpbp4.rs	0.0% <0.0%> (-15.4%)	⬇️
src/rgb/stash/anchor.rs	0.0% <0.0%> (-4.7%)	⬇️
... and 2 more

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[dr-orlovsky]

@rajarshimaitra can you also pls work on adding cases to existing tests here so we would not forget it later? (I.e. don't write new tests; just add coverage for new fields when needed if the test for other fields/structures are already in place)

UPD: if this is already done, just let me know and I will merge