Flippando - the game

[irreverentsimplicity]

This PR integrates the Flippando gno files into the main gnoland repository.

Packages added:

• flippandoserver.gno (basic game creation, unopinionated server of pairs consisting of random numbers)

Realms added:

• flippando.gno (main entry point, game mechanics, wrapper for some calls on the other realms)
• basicNFT.gno (creation of a basic NFT)
• compositeNFT.gno (creation of a composite NFT from basic NFTs)
• token.gno (FLIP fungible token creation and management)
• marketplace.gno (listing / selling basic and composite NFTs)
• airdrop.gno (managing airdrops of basicNFTs, including minting FLIP fungible tokens for airdrop account)
• flippandosvg.gno (generating various SVG images for the basic NFTs, i.e. colored squares, dices, hexagrams)
• marshals.gno (JSON marshaling functions for flippando objects and API responses)
• errors.gno (basic error types)
• util.gno (utility functions, parsing, marshaling support, etc)

Relevant packages used: avl.Tree, grc20, grc721.

AFAIK, no breaking changes have been introduced.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 60.15%. Comparing base (bd99fbe) to head (e6de200).
Report is 23 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2648      +/-   ##
==========================================
- Coverage   60.16%   60.15%   -0.01%     
==========================================
  Files         561      562       +1     
  Lines       74999    75455     +456     
==========================================
+ Hits        45120    45387     +267     
- Misses      26500    26670     +170     
- Partials     3379     3398      +19     

Flag	Coverage Δ
contribs/gnodev	61.40% <ø> (ø)
contribs/gnofaucet	14.46% <ø> (ø)
gno.land	64.57% <ø> (-0.18%)	⬇️
gnovm	64.27% <ø> (+0.14%)	⬆️
misc/genstd	80.54% <ø> (ø)
misc/logos	19.88% <ø> (ø)
tm2	62.05% <ø> (+0.06%)	⬆️

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[leohhhn]

Hey @irreverentsimplicity, can you please check the CI? fmt, mod tidy, and PR title are easy, just check why the examples/ tests are failing.