fix: prevent logger close recursion and unsafe writer closing

logger.go

@@ -1,6 +1,7 @@
 package slog
 
 import (
+	"errors"
 	"fmt"
 	"io"
 	"strings"
@@ -83,13 +84,18 @@ func (l *Logger) AddWriter(writer LoggerWriter) *Logger {
 	return l
 }
 func (l *Logger) Close() error {
+	var errs []error
 	for _, writer := range l.writers {
+		if writer == nil {
+			continue
+		}
 		err := writer.Close()
 		if err != nil {
-			l.Error(err)
+			errs = append(errs, err)
 		}
 	}
-	return nil
+	l.writers = nil
+	return errors.Join(errs...)
 }
 
 func (l *Logger) CreateTextWriter(w io.Writer) *LoggerTextWriter {