feat: escrowable capabilities

[dndll]

Description

This introduces an escrow macro which allows you to lock some thing in the store until some unlock predicate has passed.

This feature is something akin to a lightweight approval system and it a fairly common use case, we actually needed it elsewhere so I figured I'd contribute to this repo.

Doesn't expose external functionality as it's more an internal operation for contract developers.

~Edit: I had to make a fork and contribute this way, I have access to settings in this repo but for some reason I can't contribute directly.~

TODO:

• [x] workspace tests

[dndll]

hey @encody - Whats the nexts steps for this PR; are there other reviewers you want to add?