Refactor CSRF protection modules, make sure CSRF tokens can be up-to-date. (#19337)

Do a refactoring to the CSRF related code, remove most unnecessary functions.
Parse the generated token's issue time, regenerate the token every a few minutes.

integrations/repo_topic_test.go

@@ -10,6 +10,7 @@ import (
 	"testing"
 
 	api "code.gitea.io/gitea/modules/structs"
+
 	"github.com/stretchr/testify/assert"
 )