feat: Add NEP245 Multi Token Metadata Extension

[kuksag]

Overiew

This PR introduces interface required to implement NEP245 metadata extension

Token struct extension

In the specification it's stated:

A new attribute MUST be added to each Token struct:

type Token = {
  token_id: string,
+  token_metadata?: MTTokenMetadata,
+  base_metadata_id: string,
}

Which I haven't done on purpose.

Technically, it can be implemented using rust compile features to enable/disable code in case of implementing an extension.
But that's actually a breaking change with the code that has already implemented "core" standard.

On the other hand, having a token_id is sufficient to get related token_metadata and base_metadata_id (which forms MTTokenMetadataAll combined together) by calling mt_metadata_token_all.

Summary by CodeRabbit

• New Features

  • Introduced support for NEP-245 multi-token metadata, including contract-level, base token, and individual token metadata structures.
  • Added public access to the metadata module for managing and retrieving multi-token metadata.
  • Enabled paginated listing and retrieval of metadata for multiple tokens.
  • Improved serialization and deserialization of UTC datetime fields in metadata.

• Chores

  • Updated and refined dependencies to support new metadata features and serialization requirements.

[kuksag]

I haven't found borsh implementation for Datetime<Utc>, so I write a small wrapper. Let me know if that works for you.
Another option is to lift off #[near(serializers = [borsh])] requirements, but then anyway it will require every user to come up with some solution to store that data

[BonelessImpl]

Besides the minor test issue, the interface looks alright. No implementation seems to be available.

[kuksag]

@BonelessImpl I give up, I have no idea what to do with schemas (look at the failing build log). I've spent some time adding JsonSchema/trying to derive BorshSchema but it just doesn't work

[kuksag]

nit: perhaps implementation of borsh de-serialization should be moved to borsh-utils

[coderabbitai]

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Walkthrough

The changes introduce a new metadata module to the NEP-245 crate, implementing NEAR multi-token metadata standards with comprehensive data structures, traits, and serialization utilities. The metadata module is now publicly accessible. Additionally, the Cargo.toml file is updated to refine and expand dependencies, including new serialization and testing libraries.

Changes

File(s)	Change Summary
nep245/Cargo.toml	Expanded and refined dependencies; added new crates (borsh, chrono, serde_with, defuse-borsh-utils, schemars, hex) and enabled specific features. Introduced [dev-dependencies].
nep245/src/lib.rs	Added public exposure for the new metadata module.
nep245/src/metadata.rs	Introduced with NEP-245 metadata data structures, traits for metadata management/enumeration, and serialization utilities.

Sequence Diagram(s)

sequenceDiagram
    participant Caller
    participant Contract
    participant MetadataStore

    Caller->>Contract: mt_metadata_contract()
    Contract-->>Caller: MTContractMetadata

    Caller->>Contract: mt_metadata_token_all(token_ids)
    Contract->>MetadataStore: Fetch base & token metadata for token_ids
    MetadataStore-->>Contract: Vec<Option<MTTokenMetadataAll>>
    Contract-->>Caller: Vec<Option<MTTokenMetadataAll>>

    Caller->>Contract: mt_tokens_base_metadata_all(from_index, limit)
    Contract->>MetadataStore: Paginate base metadata
    MetadataStore-->>Contract: Vec<MTBaseTokenMetadata>
    Contract-->>Caller: Vec<MTBaseTokenMetadata>

Loading

Poem

In the meadow of code, new metadata blooms,
Traits and structs now chase away the glooms.
With timestamps wrapped and tokens tall,
Serialization’s ready for one and all.
Dependencies gathered, the toolkit grows—
A rabbit hops where NEP-245 flows!
🐇✨

---

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