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/tgtest/exchange.go

@@ -0,0 +1,57 @@
+package tgtest
+
+import (
+	"context"
+
+	"github.com/go-faster/errors"
+
+	"go.mau.fi/mautrix-telegram/pkg/gotd/bin"
+	"go.mau.fi/mautrix-telegram/pkg/gotd/crypto"
+	"go.mau.fi/mautrix-telegram/pkg/gotd/exchange"
+	"go.mau.fi/mautrix-telegram/pkg/gotd/proto/codec"
+	"go.mau.fi/mautrix-telegram/pkg/gotd/transport"
+)
+
+type exchangeConn struct {
+	transport.Conn
+}
+
+func (e exchangeConn) Recv(ctx context.Context, b *bin.Buffer) error {
+	for {
+		if err := e.Conn.Recv(ctx, b); err != nil {
+			return err
+		}
+
+		var authKeyID [8]byte
+		if err := b.PeekN(authKeyID[:], len(authKeyID)); err != nil {
+			return errors.Wrap(err, "peek id")
+		}
+		if authKeyID != [8]byte{} {
+			// TODO(tdakkota): what if client send registered auth key during key exchange?
+			buf := bin.Buffer{}
+			buf.PutInt32(-codec.CodeAuthKeyNotFound)
+
+			if err := e.Conn.Send(ctx, &buf); err != nil {
+				return errors.Wrap(err, "send")
+			}
+
+			continue
+		}
+
+		return nil
+	}
+}
+
+// exchange starts MTProto key exchange.
+func (s *Server) exchange(ctx context.Context, conn transport.Conn) (crypto.AuthKey, error) {
+	r, err := exchange.NewExchanger(conn, s.dcID).
+		WithClock(s.clock).
+		WithLogger(s.log.Named("exchange")).
+		WithRand(s.cipher.Rand()).
+		Server(s.key).Run(ctx)
+	if err != nil {
+		return crypto.AuthKey{}, err
+	}
+
+	return r.Key, nil
+}