Preserve ExitCase in resources + fix memory leak

[kubukoz]

Another stop on my "allocated is an antipattern" crusade. For previous editions, see typelevel/natchez-http4s#36 and typelevel/natchez#981.

[kubukoz]

thought: this change also avoids a memory leak on Scala 3 (due to better-monadic-for not eliminating the final map).

tl;dr previously it was

def loop = for {
  x <- fx
  _ <- (somethingSomething >> loop)
} yield ()

which desugars to

fx.flatMap { x => (somethingSomething >> loop).map(_ => ()) }

which allocates a Map node on every run and never cleans it up (the same goes for the top-level flatMap, and apparently the lambdas too).

Proof: run this for a minute or so.

//> using dep "org.typelevel::cats-effect:3.5.3"
import cats.effect.*

def loop: IO[Unit] = for {
  _ <- IO.unit
  _ <- IO.unit >> loop
} yield ()

object CatsDemo extends IOApp.Simple {
  def run = loop
}

[kubukoz]

thought: special case here: everywhere else we have an ExitCase to propagate, but the reaper deliberately closes resources out of thin air: I figured Succeeded makes the most sense for a resource that's no longer necessary. Canceled didn't sound right, but happy to discuss if anyone disagrees