Use nano-second time stamp granularity in the debug log

It's overkill for most purposes, but I'd say it doesn't hurt to have the
extra resolution available in the raw JSON data for the few cases where
it's useful. Have "lazygit -l" print them with milli-second resolution;
that seems to be a good middle ground.

pkg/logs/tail/tail.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"log"
 	"os"
+	"time"
 
 	"github.com/aybabtme/humanlog"
 )
@@ -15,6 +16,7 @@ func TailLogs(logFilePath string) {
 
 	opts := humanlog.DefaultOptions
 	opts.Truncates = false
+	opts.TimeFormat = time.StampMilli
 
 	_, err := os.Stat(logFilePath)
 	if err != nil {