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/peers/atomic.go

@@ -0,0 +1,20 @@
+package peers
+
+import (
+	"go.uber.org/atomic"
+
+	"go.mau.fi/mautrix-telegram/pkg/gotd/tg"
+)
+
+type atomicUser struct {
+	value atomic.Value // holds *tg.User
+}
+
+func (u *atomicUser) Load() (*tg.User, bool) {
+	v, ok := u.value.Load().(*tg.User)
+	return v, ok
+}
+
+func (u *atomicUser) Store(user *tg.User) {
+	u.value.Store(user)
+}