Replace custom Go formatter with golangci-lint fmt (#37194)

Use `golangci-lint fmt` to format code, replacing the previous custom
formatter tool. https://github.com/daixiang0/gci is used to order the
imports.

`make fmt` performs ~13% faster while consuming ~57% less cpu while
formatting for me.

`GOFUMPT_PACKAGE` is gone because it's using the builtin package from
golangci-lint.

Co-authored-by: Claude (claude-opus-4-6) <noreply@anthropic.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

modules/graceful/manager_windows.go

@@ -1,5 +1,6 @@
 // Copyright 2019 The Gitea Authors. All rights reserved.
 // SPDX-License-Identifier: MIT
+
 // This code is heavily inspired by the archived gofacebook/gracenet/net.go handler
 
 //go:build windows