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/crypto/rand.go

@@ -0,0 +1,53 @@
+package crypto
+
+import (
+	"io"
+
+	"go.mau.fi/mautrix-telegram/pkg/gotd/bin"
+)
+
+// RandInt64n returns random int64 from randSource in [0; n).
+func RandInt64n(randSource io.Reader, n int64) (int64, error) {
+	v, err := RandInt64(randSource)
+	if err != nil {
+		return 0, err
+	}
+	if v < 0 {
+		v *= -1
+	}
+	return v % n, nil
+}
+
+// RandInt64 returns random int64 from randSource.
+func RandInt64(randSource io.Reader) (int64, error) {
+	var buf [bin.Word * 2]byte
+	if _, err := io.ReadFull(randSource, buf[:]); err != nil {
+		return 0, err
+	}
+	b := &bin.Buffer{Buf: buf[:]}
+	return b.Long()
+}
+
+// RandInt128 generates and returns new random 128-bit integer.
+//
+// Use crypto/rand.Reader as randSource in production.
+func RandInt128(randSource io.Reader) (bin.Int128, error) {
+	var buf [bin.Word * 4]byte
+	if _, err := io.ReadFull(randSource, buf[:]); err != nil {
+		return bin.Int128{}, err
+	}
+	b := &bin.Buffer{Buf: buf[:]}
+	return b.Int128()
+}
+
+// RandInt256 generates and returns new random 256-bit integer.
+//
+// Use crypto/rand.Reader as randSource in production.
+func RandInt256(randSource io.Reader) (bin.Int256, error) {
+	var buf [bin.Word * 8]byte
+	if _, err := io.ReadFull(randSource, buf[:]); err != nil {
+		return bin.Int256{}, err
+	}
+	b := &bin.Buffer{Buf: buf[:]}
+	return b.Int256()
+}