refactor(metadata): merge nftMetadata into struct IPMetadata

[sebsadface]

Description

This PR merges nftMetadata into struct IPMetadata for better readability and parameter handling. The updated IPMetadata struct is:

struct IPMetadata {
  string ipMetadataURI;
  bytes32 ipMetadataHash;
  string nftMetadataURI;
  bytes32 nftMetadataHash;
}

Key Changes

• Refactor SPG function parameters to use the merged IPMetadata struct.
• Update parameter names in SPGNFT for consistency.
• Update tests to align with the new SPG function parameters.

Test Plan

All existing tests pass locally.

Notes

This change affects the IStoryProtocolGateway interface. Make sure all function calls are updated accordingly.