Reduce CPU load

`Fiber.yield` sleeps for 0 seconds. When used in a loop, this,
effectively, maxes out CPU if there are no other resumable fibers.

CHANGELOG.md

@@ -5,6 +5,11 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
 and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
 
+## [Unreleased] - 
+
+### Fixed
+- Replace `Fiber.yield` with `sleep 1.microsecond` in loops to reduce CPU load
+
 ## [1.0.0] - 2023-05-29
 
 ### Added

src/pond.cr

@@ -42,7 +42,7 @@ class Pond
     return unless @done == false
 
     until size == 0
-      Fiber.yield
+      sleep 1.microsecond
     end
 
     sync do
@@ -51,7 +51,7 @@ class Pond
     end
 
     until @done
-      Fiber.yield
+      sleep 1.microsecond
     end
   end
 
@@ -73,7 +73,7 @@ class Pond
     spawn do
       until @done.nil?
         sync { @fibers.reject!(&.dead?) }
-        Fiber.yield
+        sleep 1.microsecond
       end
 
       sync do