Incomplete sync support

[maxhollmann]

I haven't checked all places, but at least the Cron plugin doesn't have non-async methods to schedule tasks. Is full sync support something that's planned / would PRs in that direction be welcome?

[TkTech]

PRs would definitely be welcomed! Chancy is async-first, and I personally use it almost entirely within an async context with some pushes from legacy code. So, I tend to add the parallel sync interfaces only as-needed.