token-sdk updates - token fetcher overrides, metaplex provider load options

[terranmoccasin]

Updates for token-sdk

• Adding handling of Metaplex bug where invalid fetch method is being used for downloading offchain JSON
• Adding type for Overrides
• Adding handling of overrides in TokenRepository
• Adding loadImage option for MetaplexProvider. Metaplex data contains a reference to offchain JSON. The JSON loading is slow even when batched, and it is only used to populate image. Adding this flag allows usage without resolving the offchain JSON for speed improvements. This is useful for services that don't care about the image and only need decimals, symbol, etc.
• TokenRepository updates - removing TokenFetcher as a dependency and passing in as param for fetch methods. Get methods renamed to fetch.

[terranmoccasin]

Thanks Meep!

Hey @yugure-orca - Heads up that I'm going to merge this first and publish a beta version of the token-sdk for use in my other patches. Let me know if you'd like any changes when you get a chance to review, and I'm happy to open another PR to address those!

Specifically, it would be great to see if the changes to MetadataProvider in the SDK work when using in the frontend.