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/tdsync/cancel_group_test.go

@@ -0,0 +1,22 @@
+package tdsync
+
+import (
+	"context"
+	"testing"
+
+	"github.com/go-faster/errors"
+)
+
+func TestCancellableGroup(t *testing.T) {
+	g := NewCancellableGroup(context.Background())
+
+	g.Go(func(ctx context.Context) error {
+		<-ctx.Done()
+		return ctx.Err()
+	})
+
+	g.Cancel()
+	if err := g.Wait(); !errors.Is(err, context.Canceled) {
+		t.Error(err)
+	}
+}