feat(examples): openocean

[Molaryy]

This PR integrates the Openocean gno files into the main gnoland repository.
I created this project alongside Alex to learn more about nfts for our program student.

You can find a link for the dapp here: https://gnopenocean.netlify.app/ , we still have a few fix to do when a user needs to switch network but overall it works pretty fine.

Packages added:

• collection.gno (all the collections handlers and functions)
• nft.gno (basic nft functions)

---

Realms added:

• openocean.gno (basically where all the functions required for a marketplace are)

---

Relevant packages used:

• avl
• grc721
• errors
• ufmt

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 60.15%. Comparing base (0ef28e8) to head (bc610fa).
Report is 89 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2678      +/-   ##
==========================================
+ Coverage   60.13%   60.15%   +0.02%     
==========================================
  Files         560      561       +1     
  Lines       74911    74999      +88     
==========================================
+ Hits        45046    45117      +71     
- Misses      26490    26504      +14     
- Partials     3375     3378       +3     

Flag	Coverage Δ
contribs/gnodev	61.40% <ø> (ø)
contribs/gnofaucet	14.46% <ø> (-0.86%)	⬇️
gno.land	64.75% <ø> (+0.56%)	⬆️
gnovm	64.13% <ø> (ø)
misc/genstd	80.54% <ø> (ø)
misc/logos	20.23% <ø> (ø)
tm2	62.05% <ø> (+0.06%)	⬆️

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[thehowl]

@moul @zivkovicmilos how do you think we should proceed with this?

[n0izn0iz]

This architecture is not a good nft marketplace example IMO:

• The marketplace (openocean realm) should operate on the grc721 interface and not a specific collection/nft implemementation
• It should only expose marketplace related calls (Sell/Buy/Offer/etc..) and not the underlying grc721 methods
• The marketplace should use some kind of grc721 registry to access collections (see grc20reg for a registry example)
• The marketplace should keep the nfts on sale in escrow

[n0izn0iz]

this is insecure, use std.PrevRealm().Addr() instead of std.GetOrigCaller()
see https://docs.gno.land/concepts/effective-gno#contract-level-access-control