move gotd fork into repo. (#111)

- update to latest telegram layer
- remove some references to fields in tg.Entities that don't exist in
the schema
- originally added here:
https://github.com/beeper/td/commit/820929062a2ba0104397bc01235ab58a9cff780e
  - referenced here
-
https://github.com/mautrix/telegramgo/commit/124f0967ed195b5a380c9bd02e170ada9710dde3
-
https://github.com/mautrix/telegramgo/commit/4205047aab2e0639217148b5d125bfaab668bd8e

pkg/gotd/testutil/external.go

@@ -0,0 +1,38 @@
+package testutil
+
+import (
+	"os"
+	"runtime"
+	"strconv"
+	"strings"
+	"testing"
+)
+
+// SkipExternal skips current test if GOTD_TEST_EXTERNAL is not 1.
+//
+// Caller should be high-level test function with TestExternalE2E prefix,
+// like TestExternalE2EConnect.
+//
+// Run all tests with following command in module root:
+//
+//	GOTD_TEST_EXTERNAL=1 go test -v -run ^TestExternalE2E ./...
+func SkipExternal(tb testing.TB) {
+	const env = "GOTD_TEST_EXTERNAL"
+
+	tb.Helper()
+
+	{
+		// Checking caller prefix.
+		const expectedPrefix = "TestExternalE2E"
+		pc, _, _, _ := runtime.Caller(1)
+		details := runtime.FuncForPC(pc)
+		name := details.Name()[strings.LastIndex(details.Name(), ".")+1:]
+		if !strings.HasPrefix(name, expectedPrefix) {
+			tb.Fatalf("Test function %s should have prefix %s.", name, expectedPrefix)
+		}
+	}
+
+	if ok, _ := strconv.ParseBool(os.Getenv(env)); !ok {
+		tb.Skipf("Skipped. Set %s=1 to enable external e2e test.", env)
+	}
+}