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-core/src/leann/api.py

@@ -10,7 +10,7 @@ import time
 import warnings
 from dataclasses import dataclass, field
 from pathlib import Path
-from typing import Any, Literal
+from typing import Any, Literal, Optional
 
 import numpy as np
 
@@ -33,7 +33,7 @@ def compute_embeddings(
     model_name: str,
     mode: str = "sentence-transformers",
     use_server: bool = True,
-    port: int | None = None,
+    port: Optional[int] = None,
     is_build=False,
 ) -> np.ndarray:
     """
@@ -175,7 +175,7 @@ class LeannBuilder:
         self,
         backend_name: str,
         embedding_model: str = "facebook/contriever",
-        dimensions: int | None = None,
+        dimensions: Optional[int] = None,
         embedding_mode: str = "sentence-transformers",
         **backend_kwargs,
     ):