Add config module for testable path abstraction

Introduces Config dataclass with container-specific paths (user_environ,
pylint/mypy configs, user home) and drop_uid/drop_gid settings.
Provides get_config(), set_config(), and override_config() context manager
to enable testing without requiring a container environment.

Author: Nils Bars

ref_utils/config.py

@@ -0,0 +1,53 @@
+"""Configuration module for ref-utils with testable path abstraction."""
+from contextlib import contextmanager
+from contextvars import ContextVar
+from dataclasses import dataclass, field
+from pathlib import Path
+from typing import Generator
+
+
+@dataclass
+class Config:
+    """Configuration for ref-utils paths and constants.
+
+    All container-specific paths are configurable here to enable testing
+    without requiring a container environment.
+    """
+
+    user_environ_path: Path = field(default_factory=lambda: Path("/tmp/.user_environ"))
+    pylint_config_path: Path = field(default_factory=lambda: Path("/etc/pylintrc"))
+    mypy_config_path: Path = field(default_factory=lambda: Path("/etc/mypyrc"))
+    user_home_path: Path = field(default_factory=lambda: Path("/home/user"))
+    drop_uid: int = 9999
+    drop_gid: int = 9999
+
+
+# Context variable for thread-safe config override
+_config_var: ContextVar[Config] = ContextVar("config", default=Config())
+
+
+def get_config() -> Config:
+    """Get the current configuration."""
+    return _config_var.get()
+
+
+def set_config(config: Config) -> None:
+    """Set the global configuration."""
+    _config_var.set(config)
+
+
+@contextmanager
+def override_config(config: Config) -> Generator[Config, None, None]:
+    """Context manager for temporarily overriding config (useful for testing).
+
+    Args:
+        config: The temporary configuration to use.
+
+    Yields:
+        The provided config object.
+    """
+    token = _config_var.set(config)
+    try:
+        yield config
+    finally:
+        _config_var.reset(token)