feat(ucn): add pail based UCN

[hannahhoward]

Goals

Provide an out of box way to use Pail with UCAN authorized merkle clocks by expanding the UCN package to support not only raw values but actual pail data structures (and a generics package for future UCN based implementations)

Implementation

We also extract core name/revision logic to a generic

Then we provide a backward compatible implementation of the original package using that generic (a bit messy but didn't want to mess with a breaking change for now)

Then we build a Pail based version of UCN mixing Pail + UCN logic>

The core technique here utilizes the basic logic from Pail's CRDT package, but paired down to it's key contribution -- the "root" method that extracts the current CID from the merkle clock head.

Like the root package, Revisions are not mean to be values until they're realized via Value.from

Like all pail methods you get a diff of blocks -- additions and removals -- whose persistence is left as a separate concern.

For discussion

Still needs tests and some export adjustments, but I like the basic seperate of concerns -- though there remains some weird cross package imports (at this point, I think pail's clock stuff should probably live inside of.... w3clock)