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/auth/auth.go

@@ -0,0 +1,23 @@
+// Package auth provides authentication on top of tg.Client.
+package auth
+
+import (
+	"go.mau.fi/mautrix-telegram/pkg/gotd/tgerr"
+)
+
+// IsKeyUnregistered reports whether err is AUTH_KEY_UNREGISTERED error.
+//
+// Deprecated: use IsUnauthorized.
+func IsKeyUnregistered(err error) bool {
+	return tgerr.Is(err, "AUTH_KEY_UNREGISTERED")
+}
+
+// IsUnauthorized reports whether err is any 401 UNAUTHORIZED or is a 406
+// NOT_ACCEPTABLE with AUTH_KEY_DUPLICATED.
+//
+// https://core.telegram.org/api/errors#401-unauthorized
+// https://core.telegram.org/api/errors#406-not-acceptable
+func IsUnauthorized(err error) bool {
+	return tgerr.IsCode(err, 401) ||
+		(tgerr.IsCode(err, 406) && tgerr.Is(err, "AUTH_KEY_DUPLICATED"))
+}