Refactor routing_params test and isolate HTTP response tests (#1088)

* Refactor routing_params test and isolate HTTP response tests

- Moved tests that depend solely on `crow::response` from unittest.cpp
  to tests/unit_tests/test_http_response.cpp for clearer separation of concerns.
- Renamed the original "simple_response_routing_params" test in
  unittest.cpp to "routing_params" to reflect this chage.

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Co-authored-by: gittiver <[email protected]>

Author: nicholashanson