Revert "Use Go 1.19 atomics"

This reverts commit 86ffb019e1.

Given https://github.com/jackc/pgx/issues/1354 the temporary dependency
on go.uber.org/atomic for Go 1.18 support is worthwhile.

go.mod

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

go.sum

@@ -8,6 +8,8 @@ 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"
 )