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/telegram/downloader/stream_reader.go

@@ -0,0 +1,49 @@
+package downloader
+
+import (
+	"context"
+	"io"
+
+	"go.mau.fi/mautrix-telegram/pkg/gotd/tg"
+)
+
+type streamReader struct {
+	ctx      context.Context
+	reader   *reader
+	curBlock block
+	last     bool
+}
+
+var _ io.Reader = (*streamReader)(nil)
+
+func (s *streamReader) Read(p []byte) (n int, err error) {
+	select {
+	case <-s.ctx.Done():
+		return 0, s.ctx.Err()
+	default:
+	}
+
+	if len(s.curBlock.data) == 0 {
+		if s.last {
+			return 0, io.EOF
+		} else {
+			s.curBlock, err = s.reader.Next(s.ctx)
+			if err != nil {
+				return 0, err
+			}
+			s.last = s.curBlock.last()
+		}
+	}
+
+	n = copy(p, s.curBlock.data)
+	s.curBlock.data = s.curBlock.data[n:]
+	return
+}
+
+func (d *Downloader) streamToReader(ctx context.Context, r *reader) (tg.StorageFileTypeClass, io.Reader, error) {
+	first, err := r.Next(ctx)
+	if err != nil {
+		return nil, nil, err
+	}
+	return first.tag, &streamReader{ctx, r, first, first.last()}, nil
+}