feat: support token id in balances and holders endpoints

[vernonjohnson]

@iuwqyir

• Added the balances endpoint w/out type in path
• Added support for token_ids param in balances and holders endpoints (e.g., "1,2,3")
• Made token type optional for balances endpoint, so you can get all tokens

[vernonjohnson]

@iuwqyir I think for token type we should make it an array? so you could do erc1155,erc721 in one query?

[iuwqyir]

@iuwqyir I think for token type we should make it an array? so you could do erc1155,erc721 in one query?

Yes, that would be good

[iuwqyir]

Overall lgtm, just the 2 nits