feat(devnet): pop-api + non-fungibles use case

[chungquantin]

• Finalize the spec

pallet + pop-api

• chore: non-fungible use case integration test #334
• feat(devnet): runtime non-fungible pallet (basic standard features) #261
• feat(devnet): runtime non-fungibles extensions #266
• feat(devnet): pop-api methods for non-fungible use case #336
• feat(nfts): add nonfungibles runtime implementation #339

example contracts

• chore: psp34 example contract  #333

pop-drink

• feat: NonFungiblesApi trait and implementation for the Session pop-drink#21