Remove `chained.ts`

[matheus23]

I'm re-working the public API. The main goal of this is to reduce & streamline the public API surface again. The first thing on the chopping block is the Chained type. It had a couple of problems:

• Its name is horrible
• It's yet another thing you need to call to verify your UCAN, which means all of these verifications are spread across Chained.fromToken, token.validate and the capabilities function.
• It forces the whole token to be loaded & parsed. Ideally we'd lazily request proofs in UCANs depending on what capabilities we're looking for. What to us might seem like a partially invalid UCAN should still be accepted even if one of the proofs can't be parsed. (I know I wrote that thing in the first place :P)

Now that Chained is gone, some things suck a little more. Some functions became async because they can't take the pre-processed Chained type again, but need to actually do the processing themselves, which is async. It's most awkward in the delegateCapability function in the builder, which is now async. But don't worry! I have a plan on how to get it sync again! (and remove the awkwardness).

The whole API rework is probably going to be split into two PRs, this one and another one based on this. I'm hoping this will make it easier to review them independently.

[matheus23]

Closing in favor of #79. This shouldn't be release on its own, so why make it a separate PR?

@dholms I really recommend checking out #79 instead. And I'm sorry that it's a 1.5k lines diff. I did some reworking :sweat_smile:

I tried to keep the diffs smaller by splitting the PRs up, but it's hard to meaningfully split them up. I wouldn't want this version of the chopped public API published, but I would want the other version of the public API published :+1:

[dholms]

kk makes sense. i'll take a look 👀