Revert "Revert "Use Go 1.19 atomics""

This reverts commit fc4042cf23.

With the release of Go 1.20, we can use the better atomics in Go 1.19
and remove the external dependency.

go.mod

@@ -1,11 +1,8 @@
 module github.com/jackc/puddle/v2
 
-go 1.18
+go 1.19
 
-require (
-	github.com/stretchr/testify v1.8.0
-	go.uber.org/atomic v1.10.0
-)
+require github.com/stretchr/testify v1.8.0
 
 require (
 	github.com/davecgh/go-spew v1.1.1 // indirect

go.sum

@@ -8,8 +8,6 @@ github.com/stretchr/objx v0.4.0/go.mod h1:YvHI0jy2hoMjB+UWwv71VJQ9isScKT/TqJzVSS
 github.com/stretchr/testify v1.7.1/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
 github.com/stretchr/testify v1.8.0 h1:pSgiaMZlXftHpm5L7V1+rVB+AZJydKsMxsQBIJw4PKk=
 github.com/stretchr/testify v1.8.0/go.mod h1:yNjHg4UonilssWZ8iaSj1OCr/vHnekPRkoO+kdMU+MU=
-go.uber.org/atomic v1.10.0 h1:9qC72Qh0+3MqyJbAn8YU5xVq1frD8bn3JtD2oXtafVQ=
-go.uber.org/atomic v1.10.0/go.mod h1:LUxbIzbOniOlMKjJjyPfpl4v+PKK2cNJn91OQbhoJI0=
 golang.org/x/sync v0.0.0-20220923202941-7f9b1623fab7 h1:ZrnxWX62AgTKOSagEqxvb3ffipvEDX2pl7E1TdqLqIc=
 golang.org/x/sync v0.0.0-20220923202941-7f9b1623fab7/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=

pool.go

@@ -4,10 +4,10 @@ import (
 	"context"
 	"errors"
 	"sync"
+	"sync/atomic"
 	"time"
 
 	"github.com/jackc/puddle/v2/internal/genstack"
-	"go.uber.org/atomic"
 	"golang.org/x/sync/semaphore"
 )