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/testutil/alloc.go

@@ -0,0 +1,23 @@
+package testutil
+
+import "testing"
+
+const defaultAllocRuns = 10
+
+// MaxAlloc checks that f does not allocate more than n.
+func MaxAlloc(t *testing.T, n int, f func()) {
+	t.Helper()
+	if Race {
+		t.Skip("Skipped (race detector conflicts with allocation tests)")
+	}
+	avg := testing.AllocsPerRun(defaultAllocRuns, f)
+	if avg > float64(n) {
+		t.Errorf("Allocated %f bytes per run, expected less than %d", avg, n)
+	}
+}
+
+// ZeroAlloc checks that f does not allocate.
+func ZeroAlloc(t *testing.T, f func()) {
+	t.Helper()
+	MaxAlloc(t, 0, f)
+}