fix: Python 3.9 compatibility - replace Union type syntax

- Replace 'int | None' with 'Optional[int]' everywhere
- Replace 'subprocess.Popen | None' with 'Optional[subprocess.Popen]'
- Add Optional import to all affected files
- Update ruff target-version from py310 to py39
- The '|' syntax for Union types was introduced in Python 3.10 (PEP 604)

Fixes TypeError: unsupported operand type(s) for |: 'type' and 'NoneType'

packages/leann-backend-diskann/leann_backend_diskann/diskann_backend.py

@@ -4,7 +4,7 @@ import os
 import struct
 import sys
 from pathlib import Path
-from typing import Any, Literal
+from typing import Any, Literal, Optional
 
 import numpy as np
 import psutil
@@ -384,7 +384,7 @@ class DiskannSearcher(BaseSearcher):
         prune_ratio: float = 0.0,
         recompute_embeddings: bool = False,
         pruning_strategy: Literal["global", "local", "proportional"] = "global",
-        zmq_port: int | None = None,
+        zmq_port: Optional[int] = None,
         batch_recompute: bool = False,
         dedup_node_dis: bool = False,
         **kwargs,