Fix compatibility with Python 3.14.0a1 (#848)

typing.ByteString has been removed from Python 3.14.
Ported the suggested way from the documentation:
https://docs.python.org/3.13/library/typing.html#typing.ByteString

src/nacl/bindings/crypto_secretstream.py

@@ -11,7 +11,7 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
-from typing import ByteString, Optional, Tuple, cast
+from typing import Optional, Tuple, Union, cast
 
 from nacl import exceptions as exc
 from nacl._sodium import ffi, lib
@@ -73,6 +73,7 @@ class crypto_secretstream_xchacha20poly1305_state:
 
     def __init__(self) -> None:
         """Initialize a clean state object."""
+        ByteString = Union[bytes, bytearray, memoryview]
         self.statebuf: ByteString = ffi.new(
             "unsigned char[]",
             crypto_secretstream_xchacha20poly1305_STATEBYTES,

tests/test_secretstream.py

@@ -16,7 +16,7 @@
 import json
 import os
 import random
-from typing import ByteString, List, Optional, Tuple
+from typing import List, Optional, Tuple, Union
 
 from _pytest._code import ExceptionInfo
 from _pytest.monkeypatch import MonkeyPatch
@@ -219,6 +219,7 @@ def test_it_like_libsodium():
 
     header = crypto_secretstream_xchacha20poly1305_init_push(state, k)
 
+    ByteString = Union[bytes, bytearray, memoryview]
     state_save: ByteString = ffi.buffer(state.statebuf)[:]
 
     c1 = crypto_secretstream_xchacha20poly1305_push(