revert: tea 1.0 rewrite (#1122–#1126) (#1146)

Reverts #1126, #1125, #1124, #1123 and #1122.

`go.mod` keeps the Go 1.26 line with toolchain `go1.26.9` (instead of the original `go1.26.6`) so the security fix from #1131 isn't lost.

reopens #69
reopens #141
reopens #162
reopens #172
reopens #197
reopens #232
reopens #240
reopens #246
reopens #323
reopens #325
reopens #326
reopens #328
reopens #344
reopens #351
reopens #373
reopens #403
reopens #406
reopens #417
reopens #430
reopens #457
reopens #480
reopens #482
reopens #489
reopens #490
reopens #498
reopens #500
reopens #504
reopens #510
reopens #516
reopens #523
reopens #556
reopens #560
reopens #569
reopens #571
reopens #602
reopens #632
reopens #633
reopens #643
reopens #666
reopens #670
reopens #672
reopens #677
reopens #683
reopens #697
reopens #726
reopens #737
reopens #770
reopens #779
reopens #804
reopens #817
reopens #831
reopens #833
reopens #834
reopens #908
reopens #966
reopens #1023
reopens #1029
reopens #1032
reopens #1050
reopens #1052
reopens #1069
reopens #1073
reopens #1087
reopens #1091
reopens #1094
reopens #1110
reopens #1115
reopens #1116
reopens #1118

Reviewed-on: https://gitea.com/gitea/tea/pulls/1146
Reviewed-by: TheFox0x7 <95654+thefox0x7@noreply.gitea.com>

modules/filelock/filelock_unix.go

@@ -0,0 +1,39 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+//go:build unix
+
+package filelock
+
+import (
+	"fmt"
+	"os"
+	"syscall"
+	"time"
+)
+
+// lockFile acquires an exclusive lock on the file using flock.
+// It polls with non-blocking flock until timeout.
+func lockFile(file *os.File, timeout time.Duration) error {
+	deadline := time.Now().Add(timeout)
+
+	for {
+		err := syscall.Flock(int(file.Fd()), syscall.LOCK_EX|syscall.LOCK_NB)
+		if err == nil {
+			return nil
+		}
+		if err != syscall.EWOULDBLOCK {
+			return fmt.Errorf("flock failed: %w", err)
+		}
+
+		if time.Now().After(deadline) {
+			return fmt.Errorf("timeout waiting for file lock")
+		}
+		time.Sleep(FileLockPollInterval)
+	}
+}
+
+// unlockFile releases the lock on the file.
+func unlockFile(file *os.File) error {
+	return syscall.Flock(int(file.Fd()), syscall.LOCK_UN)
+}