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/proto/unencrypted_message.go

@@ -0,0 +1,55 @@
+package proto
+
+import (
+	"github.com/go-faster/errors"
+
+	"go.mau.fi/mautrix-telegram/pkg/gotd/bin"
+)
+
+// UnencryptedMessage is plaintext message.
+type UnencryptedMessage struct {
+	MessageID   int64
+	MessageData []byte
+}
+
+// Decode implements bin.Decoder.
+func (u *UnencryptedMessage) Decode(b *bin.Buffer) error {
+	{
+		// Reading auth_key_id that should be always equal to zero.
+		id, err := b.Long()
+		if err != nil {
+			return err
+		}
+		if id != 0 {
+			return errors.Errorf("unexpected auth_key_id %d of plaintext message", id)
+		}
+	}
+	{
+		v, err := b.Long()
+		if err != nil {
+			return err
+		}
+		u.MessageID = v
+	}
+
+	// Reading data.
+	dataLen, err := b.Int32()
+	if err != nil {
+		return err
+	}
+	u.MessageData = append(u.MessageData[:0], make([]byte, dataLen)...)
+	if err := b.ConsumeN(u.MessageData, int(dataLen)); err != nil {
+		return errors.Wrap(err, "consume payload")
+	}
+
+	return nil
+}
+
+// Encode implements bin.Encoder.
+func (u UnencryptedMessage) Encode(b *bin.Buffer) error {
+	b.PutLong(0)
+	b.PutLong(u.MessageID)
+	b.PutInt32(int32(len(u.MessageData)))
+	b.Put(u.MessageData)
+	return nil
+}