Queue state observability API

[sureshg]

This library looks interesting. Right now there's no way to see what's in the queue without hitting the database directly. It'd be useful to have count(pKind), list(pKind, limit, offset), and cancel(pKey, pKind) so teams can check queue depth, see what's pending, and drop entries when needed, without coupling to the underlying table schema.

[alexandru]

Addressed in comment: #25 (comment)