test: add initial unit tests for argument_parser module

Add comprehensive test suite for the argument_parser module including:
- Tests for _convert_to_bool with truthy/falsy values
- Tests for _convert_to_list with JSON and comma-separated inputs
- Tests for _convert_to_dict with valid/invalid JSON
- Tests for convert_string_to_type with various type annotations
- Tests for convert_arguments with typed functions
- Tests for ArgumentConversionError exception class

This establishes the foundation for the project's test infrastructure
with pytest configuration already in place.

tests/conftest.py

@@ -0,0 +1,31 @@
+"""Pytest configuration and shared fixtures for Strix tests."""
+
+import pytest
+
+
+@pytest.fixture
+def sample_function_with_types():
+    """Create a sample function with type annotations for testing argument conversion."""
+
+    def func(
+        name: str,
+        count: int,
+        enabled: bool,
+        ratio: float,
+        items: list,
+        config: dict,
+        optional: str | None = None,
+    ) -> None:
+        pass
+
+    return func
+
+
+@pytest.fixture
+def sample_function_no_annotations():
+    """Create a sample function without type annotations."""
+
+    def func(arg1, arg2, arg3):
+        pass
+
+    return func