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_test.go

@@ -0,0 +1,61 @@
+package tgtest
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	"github.com/go-faster/errors"
+	"github.com/stretchr/testify/assert"
+
+	"go.mau.fi/mautrix-telegram/pkg/gotd/bin"
+	"go.mau.fi/mautrix-telegram/pkg/gotd/proto/codec"
+	"go.mau.fi/mautrix-telegram/pkg/gotd/tdsync"
+	"go.mau.fi/mautrix-telegram/pkg/gotd/transport"
+)
+
+func Test_exchangeConn_Recv(t *testing.T) {
+	a := assert.New(t)
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	defer cancel()
+
+	i := transport.Intermediate
+	c1, c2 := i.Pipe()
+	defer func() {
+		a.NoError(c1.Close())
+		a.NoError(c2.Close())
+	}()
+	e := exchangeConn{Conn: c1}
+
+	s := "abcdabcd"
+	a.Len(s, 8)
+
+	grp := tdsync.NewCancellableGroup(ctx)
+	grp.Go(func(ctx context.Context) error {
+		b := bin.Buffer{Buf: []byte(s)}
+		if err := c2.Send(ctx, &b); err != nil {
+			return err
+		}
+
+		b.Reset()
+		var protocolErr *codec.ProtocolErr
+		if err := c2.Recv(ctx, &b); err != nil && !errors.As(err, &protocolErr) {
+			return err
+		}
+
+		b.ResetN(8)
+		b.Put([]byte(s))
+		if err := c2.Send(ctx, &b); err != nil {
+			return err
+		}
+
+		return nil
+	})
+
+	var b bin.Buffer
+	a.NoError(e.Recv(ctx, &b))
+	b.Skip(8)
+	a.Equal(s, string(b.Buf))
+
+	a.NoError(grp.Wait())
+}