refactor: implement generic optional import mechanisms

this project is actively using optional imports, which leads to
duplicate handling here and there. This commit implements logic in
special method to reduce complexity and simplify tests paths

ahriman-core/tests/ahriman/core/test_module_loader.py

@@ -2,7 +2,7 @@ import ahriman.web.views
 
 from pathlib import Path
 
-from ahriman.core.module_loader import _modules, implementations
+from ahriman.core.module_loader import _modules, implementations, optional_module
 from ahriman.web.views.base import BaseView
 
 
@@ -23,3 +23,17 @@ def test_implementations() -> None:
     assert routes
     assert all(isinstance(view, type) for view in routes)
     assert all(issubclass(view, BaseView) for view in routes)
+
+
+def test_optional_module() -> None:
+    """
+    must import an available module
+    """
+    assert optional_module("ahriman.web.views") is ahriman.web.views
+
+
+def test_optional_module_fallback() -> None:
+    """
+    must return none when the module cannot be imported
+    """
+    assert optional_module("missing_ahriman_module") is None