feat: Add ERC-8021 schema 2 support

[dgca]

Adds ERC-8021 Schema 2 (CBOR-encoded) attribution support to the Attribution module. This enables extensible transaction annotation with optional fields for app codes, wallet codes, custom registries, and arbitrary metadata.

Design choices that could use a second look:

• The public API uses descriptive field names (appCode, walletCode, registries, metadata) rather than the single-letter CBOR keys (a, w, r, m) from the spec. I decided to use "registries" instead of "codeRegistries" (which would align with schema 1's codeRegistry field) so the field names match the single-letter CBOR fields.
• I created a new AttributionSchemaId2Registry type even though it's the same as AttributionSchemaId1Registry to avoid confusion (e.g. SchemaId2 field using SchemaId1 type).

Example usage:

const schema2Suffix = Attribution.toDataSuffix({
  appCode: 'baseapp',
  walletCode: 'privy',
});

console.log(schema2Suffix); // 0xa261616762617365617070617765707269767900130280218021802180218021802180218021

const schema2Parsed = Attribution.fromData(schema2Suffix);

console.log(schema2Parsed); // { appCode: 'baseapp', walletCode: 'privy' }

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