Add first-class stack safety

[sbuzzard]

Currently dtrace leans on it's underlying effect for stack safety, which works ok for effects like IO that provide it but even IO is inadequate for dtrace needs as even for map/ap operations, we need that suspension because of our Kleisli-like nature (with the TC => F[?] that represents a span). So we use a bunch of hacks which generally "work" but only with a bunch of implicit constraints. I labeled this an enhancement but its really fixing an underlying design flaw.