Use type Buffer instead of Uint8Array for BTC scripts

[sisou]

Currently the ParsedBitcoinTransactionInput is typed with Uint8Array for its scripts, instead of the NodeJS-native Buffer which all BitcoinJS methods require.

This was done because Buffer is not available in a browser and the browerify-ed Buffer port uses a Uint8Array underneath anyway.

Currently this leads to type errors whenever a BitcoinJS-method is called with a Uint8Array-typed object and requires a // @ts-ignore comment.

Maybe it would be better if the objects were typed with Buffer, preventing the type errors when a method is called (everywhere in the code) and replacing them with type errors where these objects are created (in limited locations in the code).