ci(golangci-lint): update configuration and fix lint issues (#4247)

* ci: update golangci-lint configuration and lint settings

- Update golangci-lint to version 2
- Enable new linters and adjust existing ones
- Update lint settings across multiple test files
- Remove unused struct and variable checks
- Add new lint exclusions for generated code and specific directories

Signed-off-by: Flc <four_leaf_clover@foxmail.com>

* ci(github): update golangci-lint-action to v8 and lint version to v2.3.4

Signed-off-by: Flc <four_leaf_clover@foxmail.com>

* ci: downgrade golangci-lint to v2.1.6

Signed-off-by: Flc <four_leaf_clover@foxmail.com>

* ci(golangci): add gofumpt linter and fix related issues- Added gofumpt linter to .golangci.yml

Signed-off-by: Flc <four_leaf_clover@foxmail.com>

* test: ignore testifylint and gofumpt lints in specific test cases

Signed-off-by: Flc <four_leaf_clover@foxmail.com>

* build(deps): remove golang.org/x/lint

- Remove golang.org/x/lint package from go.mod
- Update related dependencies in go.sum

Signed-off-by: flc1125 <four_leaf_clover@foxmail.com>

* build(deps): downgrade golang.org/x/mod and golang.org/x/tools

- Downgrade golang.org/x/mod from v0.24.0 to v0.18.0
- Downgrade golang.org/x/tools from v0.33.0 to v.22.0

These changes are made to address compatibility issues with the current project setup.

Signed-off-by: flc1125 <four_leaf_clover@foxmail.com>

---------

Signed-off-by: Flc <four_leaf_clover@foxmail.com>
Signed-off-by: flc1125 <four_leaf_clover@foxmail.com>

tree_test.go

@@ -481,7 +481,7 @@ func TestTreeDuplicatePath(t *testing.T) {
 		}
 	}
 
-	//printChildren(tree, "")
+	// printChildren(tree, "")
 
 	checkRequests(t, tree, testRequests{
 		{"/", false, "/", nil},
@@ -532,7 +532,7 @@ func TestTreeCatchAllConflictRoot(t *testing.T) {
 
 func TestTreeCatchMaxParams(t *testing.T) {
 	tree := &node{}
-	var route = "/cmd/*filepath"
+	route := "/cmd/*filepath"
 	tree.addRoute(route, fakeHandler(route))
 }
 
@@ -692,7 +692,7 @@ func TestTreeRootTrailingSlashRedirect(t *testing.T) {
 }
 
 func TestRedirectTrailingSlash(t *testing.T) {
-	var data = []struct {
+	data := []struct {
 		path string
 	}{
 		{"/hello/:name"},