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/mtproto/mtproto_test.go

@@ -0,0 +1,60 @@
+package mtproto
+
+import (
+	"context"
+	"sync"
+
+	"github.com/go-faster/errors"
+
+	"go.mau.fi/mautrix-telegram/pkg/gotd/bin"
+)
+
+type testPayload struct {
+	Data []byte
+}
+
+func (d testPayload) Decode(b *bin.Buffer) error {
+	_, err := b.Bytes()
+	return err
+}
+
+func (d testPayload) Encode(b *bin.Buffer) error {
+	b.PutBytes(d.Data)
+	return nil
+}
+
+type noopBuf struct{}
+
+func (n noopBuf) Consume(id int64) bool {
+	return true
+}
+
+type constantConn struct {
+	data    []byte
+	cancel  context.CancelFunc
+	counter int
+	mux     sync.Mutex
+}
+
+func (c *constantConn) Send(ctx context.Context, b *bin.Buffer) error {
+	return nil
+}
+
+func (c *constantConn) Recv(ctx context.Context, b *bin.Buffer) error {
+	c.mux.Lock()
+	exit := c.counter == 0
+	if exit {
+		c.mux.Unlock()
+		c.cancel()
+		return errors.New("error")
+	}
+	c.counter--
+	c.mux.Unlock()
+
+	b.Put(c.data)
+	return nil
+}
+
+func (c *constantConn) Close() error {
+	return nil
+}