fix: Python 3.9 compatibility - replace union types and builtin generics

- Replace 'str | None' with 'Optional[str]'
- Replace 'list[str]' with 'List[str]'
- Replace 'dict[' with 'Dict['
- Replace 'tuple[' with 'Tuple['
- Add missing typing imports (List, Dict, Tuple)

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

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

uv.lock

@@ -2155,7 +2155,7 @@ wheels = [
 
 [[package]]
 name = "leann-backend-diskann"
-version = "0.2.1"
+version = "0.2.5"
 source = { editable = "packages/leann-backend-diskann" }
 dependencies = [
     { name = "leann-core" },
@@ -2167,14 +2167,14 @@ dependencies = [
 
 [package.metadata]
 requires-dist = [
-    { name = "leann-core", specifier = "==0.2.1" },
+    { name = "leann-core", specifier = "==0.2.5" },
     { name = "numpy" },
     { name = "protobuf", specifier = ">=3.19.0" },
 ]
 
 [[package]]
 name = "leann-backend-hnsw"
-version = "0.2.1"
+version = "0.2.5"
 source = { editable = "packages/leann-backend-hnsw" }
 dependencies = [
     { name = "leann-core" },
@@ -2187,7 +2187,7 @@ dependencies = [
 
 [package.metadata]
 requires-dist = [
-    { name = "leann-core", specifier = "==0.2.1" },
+    { name = "leann-core", specifier = "==0.2.5" },
     { name = "msgpack", specifier = ">=1.0.0" },
     { name = "numpy" },
     { name = "pyzmq", specifier = ">=23.0.0" },
@@ -2195,7 +2195,7 @@ requires-dist = [
 
 [[package]]
 name = "leann-core"
-version = "0.2.1"
+version = "0.2.5"
 source = { editable = "packages/leann-core" }
 dependencies = [
     { name = "accelerate" },