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.

(cherry picked from commit fb1ad920b769799aa1287441289d15477d9878c5)

Conflicts:
	modules/git/utils_test.go
	trivial context conflict because sha256 testing in Forgejo has diverged

modules/git/utils_test.go

@@ -3,7 +3,11 @@
 
 package git
 
-import "testing"
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
 
 // This file contains utility functions that are used across multiple tests,
 // but not in production code.
@@ -13,3 +17,10 @@ func skipIfSHA256NotSupported(t *testing.T) {
 		t.Skip("skipping because installed Git version doesn't support SHA256")
 	}
 }
+
+func TestHashFilePathForWebUI(t *testing.T) {
+	assert.Equal(t,
+		"8843d7f92416211de9ebb963ff4ce28125932878",
+		HashFilePathForWebUI("foobar"),
+	)
+}