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/pool/req_map.go

@@ -0,0 +1,63 @@
+package pool
+
+import (
+	"sync"
+
+	"go.uber.org/atomic"
+)
+
+type reqKey int64
+
+type reqMap struct {
+	m   map[reqKey]chan *poolConn
+	mux sync.Mutex
+	_   [4]byte
+
+	nextRequest atomic.Int64
+}
+
+func newReqMap() *reqMap {
+	return &reqMap{
+		m: map[reqKey]chan *poolConn{},
+	}
+}
+
+func (r *reqMap) request() (key reqKey, ch chan *poolConn) {
+	key = reqKey(r.nextRequest.Inc())
+	ch = make(chan *poolConn, 1)
+
+	r.mux.Lock()
+	r.m[key] = ch
+	r.mux.Unlock()
+	return key, ch
+}
+
+func (r *reqMap) transfer(c *poolConn) bool {
+	r.mux.Lock()
+	if len(r.m) < 1 { // no requests
+		r.mux.Unlock()
+		return false
+	}
+
+	var ch chan *poolConn
+	var k reqKey
+	for k, ch = range r.m { // Get one from map.
+		break
+	}
+	delete(r.m, k) // Remove from pending requests.
+	r.mux.Unlock()
+
+	if ch == nil {
+		panic("unreachable: channel can't be nil due to map not empty")
+	}
+
+	ch <- c
+	close(ch)
+	return true
+}
+
+func (r *reqMap) delete(key reqKey) {
+	r.mux.Lock()
+	delete(r.m, key)
+	r.mux.Unlock()
+}