chore: begin typing note data provider

[nventuro]

This is an initial attempt at trying to make these more readable. The technique can be trivially extended to MultiMap, but first I wanted to see how far I could take it before going all-in - for this reason I only used it in the note data provider.

It'd be very nice to also do something similar for keys, albeit in such a way where we accept anything that can be converted into a string as a key. It'd let us use AztecAddress, Fr, etc. as types, helping make sense of the types and removing a lot of toString calls that make the code hard to read and easy to misuse. However there's K extends Key constraints all over the place, so doing this might not be trivial. I gave up after some brief exploration.

[Thunkar]

Q: Wouldn't it make more sense to force our stores to only accept types that implement to/fromBuffer? Would that be too much work given we use them everywhere?

[nventuro]

Our stores don't currently force you to use Buffer, it's almost a coincidence that this is always the underlying type. Yes, we could have a thin wrapper around them with this behavior, or just change everything to use Buffer under the hood. I first wanted to see the impact of this to determine if the change was worth it.