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/rpc/errors.go

@@ -0,0 +1,26 @@
+package rpc
+
+import (
+	"fmt"
+
+	"github.com/go-faster/errors"
+)
+
+// RetryLimitReachedErr means that server does not acknowledge request
+// after multiple retries.
+type RetryLimitReachedErr struct {
+	Retries int
+}
+
+func (r *RetryLimitReachedErr) Error() string {
+	return fmt.Sprintf("retry limit reached after %d attempts", r.Retries)
+}
+
+// Is reports whether err is RetryLimitReachedErr.
+func (r *RetryLimitReachedErr) Is(err error) bool {
+	_, ok := err.(*RetryLimitReachedErr)
+	return ok
+}
+
+// ErrEngineClosed means that engine was closed.
+var ErrEngineClosed = errors.New("engine was closed")