Refactor TkClasspathTest for object-oriented exception handling and better expressiveness (relates to #1408)

The test class TkClasspathTest violates several object-oriented design principles discussed in the Pain of OOP course:

1. Procedural error handling:
   The use of Assertions.assertThrows(...) relies on capturing exceptions with lambdas, which is a procedural approach. Instead, object-based handling using something like TkFailure or RsFailure would align better with object-oriented thinking.

2. Low-level request construction:
   The test constructs fake requests using raw strings (e.g., "PUT", "/something-else"). This violates the object-oriented idea that everything is an object. Using decorators like RqWithMethod, RqWithUri improves clarity and encapsulation.

Suggested Improvements

• Replace assertThrows(...) with an object-oriented failure handling strategy where possible.
• Replace string-based request setup with composable request objects.