fix: resolve CI linting and type checking issues

config_converter/converters/base.py

@@ -2,7 +2,7 @@
 
 from abc import ABC, abstractmethod
 from pathlib import Path
-from typing import Any, Dict, Optional
+from typing import Any, Dict, Optional, Union
 
 
 class ConversionError(Exception):
@@ -18,11 +18,11 @@ class BaseConverter(ABC):
     FILE_EXTENSIONS: list[str] = []
 
     @abstractmethod
-    def read(self, source: str | Path) -> Dict[str, Any]:
+    def read(self, source: Union[str, Path]) -> Dict[str, Any]:
         """Read and parse a configuration file."""
 
     @abstractmethod
-    def write(self, data: Dict[str, Any], target: str | Path) -> None:
+    def write(self, data: Dict[str, Any], target: Union[str, Path]) -> None:
         """Write configuration data to a file."""
 
     @abstractmethod
@@ -62,7 +62,7 @@ class BaseConverter(ABC):
         return ["json", "yaml", "yml", "toml", "ini"]
 
     @classmethod
-    def guess_format(cls, filepath: str | Path) -> Optional[str]:
+    def guess_format(cls, filepath: Union[str, Path]) -> Optional[str]:
         """Guess format from file extension."""
         ext = Path(filepath).suffix.lower().lstrip(".")
         format_map: Dict[str, str] = {