Cleaning up code base, bumping to go 1.23

diff --git a/go.mod b/go.mod
index 6f3128c..70e4c73 100644
--- a/go.mod
+++ b/go.mod

@@ -1,3 +1,3 @@
 module github.com/chromedp/sysutil
 
-go 1.15
+go 1.23

diff --git a/sysutil.go b/sysutil.go
index 856a0c6..ae85057 100644
--- a/sysutil.go
+++ b/sysutil.go

@@ -1,6 +1,8 @@
 package sysutil
 
-import "time"
+import (
+	"time"
+)
 
 var btime time.Time
 
@@ -11,5 +13,5 @@
 
 // Uptime returns the duration the system has been up.
 func Uptime() time.Duration {
-	return time.Now().Sub(btime)
+	return time.Since(btime)
 }

diff --git a/sysutil_bsd.go b/sysutil_bsd.go
index 0c00c7f..c6c7448 100644
--- a/sysutil_bsd.go
+++ b/sysutil_bsd.go

@@ -1,4 +1,4 @@
-// +build darwin freebsd openbsd netbsd
+//go:build darwin || freebsd || openbsd || netbsd
 
 package sysutil
 

diff --git a/sysutil_linux.go b/sysutil_linux.go
index 66fd321..e1b02c8 100644
--- a/sysutil_linux.go
+++ b/sysutil_linux.go

@@ -1,10 +1,10 @@
-// +build linux
+//go:build linux
 
 package sysutil
 
 import (
 	"bytes"
-	"io/ioutil"
+	"os"
 	"strconv"
 	"time"
 )
@@ -15,7 +15,7 @@
 )
 
 func init() {
-	buf, err := ioutil.ReadFile("/proc/stat")
+	buf, err := os.ReadFile("/proc/stat")
 	if err != nil {
 		btime = time.Now()
 		return

diff --git a/sysutil_other.go b/sysutil_other.go
index 25e5b78..8dc9331 100644
--- a/sysutil_other.go
+++ b/sysutil_other.go

@@ -1,4 +1,4 @@
-// +build !linux,!windows,!darwin,!freebsd,!openbsd,!netbsd
+//go:build !linux && !windows && !darwin && !freebsd && !openbsd && !netbsd
 
 package sysutil
 

diff --git a/sysutil_windows.go b/sysutil_windows.go
index 6fb88c1..cc58491 100644
--- a/sysutil_windows.go
+++ b/sysutil_windows.go

@@ -1,4 +1,4 @@
-// +build windows
+//go:build windows
 
 package sysutil
 

diff --git a/timeval.go b/timeval.go
index 14a0a4a..63e0c62 100644
--- a/timeval.go
+++ b/timeval.go

@@ -1,4 +1,4 @@
-// +build openbsd netbsd
+//go:build openbsd || netbsd
 
 package sysutil
 

diff --git a/timeval32.go b/timeval32.go
index 17ad8d2..d8ce8e3 100644
--- a/timeval32.go
+++ b/timeval32.go

@@ -1,4 +1,4 @@
-// +build darwin freebsd
+//go:build darwin || freebsd
 
 package sysutil