account_group_id -> wallet

[grod220]

Closes ##2997

[hdevalence]

One thing I don't think we settled on: up to this point, the "account group ID" has been a purely internal name, only used in internal code and datastructures. Adding a Bech32 prefix for it feels like making it in some sense user-facing (at least to a subset of users).

Did we want to align on terminology first? We'd talked about having a conceptual hierarchy of "wallet" / "account" / "address" for spend capability / logical account / payment capability that we currently call "account group" / "account" / "address". Should we commit to that?

[grod220]

@hdevalence I think that terminology makes sense! There also seemed to be consensus on the team meeting with it too. Changed all instances of account group id to wallet.

[hdevalence]

I hate to ask to redo everything, but I'm wondering if we could call it WalletId rather than Wallet. It seems kind of important to have the name clarify that it's just an identifier, it doesn't actually do anything itself -- if we call it "wallet", I think someone reading the code or API docs could easily get confused thinking that it was the thing that manages funds, rather than just being an identifier.

[grod220]

I wasn't sure if this struct would be something later down the line we'd extend. I had a hunch about Id though. Wasn't terribly hard to add.

[grod220]

@hdevalence thanks for the re-review 🙏