feat: add NFT functionality

[qvkare]

Description

Refactors the NFT functionality in the Base MCP, adding proper type safety and improving the code structure. It creates dedicated directories for NFT tools and implements two main functionalities: listing NFTs owned by an address and transferring NFTs to another address.

This is a reimplementation of the previously closed PR #6 (#6).

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

How Has This Been Tested?

• Tested the NFT functionality with real wallet addresses (e.g., 0x89A93a48C6Ef8085B9d07e46AaA96DFDeC717040)
• Verified that the NFT listing operation returns expected results
• Verified that the NFT transfer operation works correctly
• Ran all lint, build, and format checks locally to ensure code quality

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

Implementation Details

• Created dedicated directories for NFT tools under src/tools/nft/
• Implemented NFT functionality with two main tools:
  • list_nfts: Lists NFTs owned by a specific address
  • transfer_nft: Transfers NFTs to another address
• Updated README.md and examples.md to include information about NFT functionalities
• Created utility functions for NFT standard detection and data formatting
• The implementation uses the Alchemy API for NFT functionality
• Each tool follows the standard pattern with dedicated files (index.ts, schemas.ts, handlers.ts)
• Improved type safety by replacing any types with proper interfaces and type definitions