Refactor sha1 and time-limited code (#31023)

Remove "EncodeSha1", it shouldn't be used as a general purpose hasher
(just like we have removed "EncodeMD5" in #28622)

Rewrite the "time-limited code" related code and write better tests, the
old code doesn't seem quite right.

modules/git/utils_test.go

@@ -0,0 +1,17 @@
+// Copyright 2024 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package git
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestHashFilePathForWebUI(t *testing.T) {
+	assert.Equal(t,
+		"8843d7f92416211de9ebb963ff4ce28125932878",
+		HashFilePathForWebUI("foobar"),
+	)
+}