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/transport/detect_codec.go

@@ -0,0 +1,35 @@
+package transport
+
+import (
+	"bytes"
+	"io"
+
+	"github.com/go-faster/errors"
+
+	"go.mau.fi/mautrix-telegram/pkg/gotd/proto/codec"
+)
+
+func detectCodec(c io.Reader) (Codec, io.Reader, error) {
+	var buf [4]byte
+	if _, err := io.ReadFull(c, buf[:1]); err != nil {
+		return nil, nil, errors.Wrap(err, "read first byte")
+	}
+
+	if buf[0] == codec.AbridgedClientStart[0] {
+		return Abridged.Codec(), c, nil
+	}
+
+	if _, err := io.ReadFull(c, buf[1:4]); err != nil {
+		return nil, nil, errors.Wrap(err, "read header")
+	}
+	switch buf {
+	case codec.IntermediateClientStart:
+		return Intermediate.Codec(), c, nil
+	case codec.PaddedIntermediateClientStart:
+		return PaddedIntermediate.Codec(), c, nil
+	default:
+		buffered := bytes.NewReader(buf[:])
+		r := io.MultiReader(buffered, c)
+		return Full.Codec(), r, nil
+	}
+}