Refactor routing_params test and isolate HTTP response tests

[nicholashanson]

Unit tests that only depend on crow::response were moved to unit_tests/test_http_response.cpp.

This is a proof-of-concept for splitting the monolithic file uinttest.cpp into multiple files that map one-to-one to files in include/crow.
The aims of this refactor are to:

• Improve the readability and maintainability of unit tests.
• Simplify onboarding for new developers.
• Enable more granular testing and improve overall test coverage.

Below is a comparison between outputs before and after the refactor to validate that only the intended changes were made.

tests/unittest:

There is one more test than before because "simple_response_routing_params" was split into "simple_response" and "routing_params".

Before:

All tests passed (872 assertions in 93 test cases)

After:

All tests passed (872 assertions in 94 test cases)

test/unittest "custom_content_type"

No change.

Before:

Filters: "custom_content_types"
Randomness seeded to: 1196796123
(2025-09-15 15:05:54) [WARNING ] Unable to interpret mime type for content type 'custom/type'. Defaulting to text/plain.
(2025-09-15 15:05:54) [WARNING ] Unable to interpret mime type for content type 'notarealextension'. Defaulting to text/plain.
(2025-09-15 15:05:54) [WARNING ] Unable to interpret mime type for content type 'image/'. Defaulting to text/plain.
(2025-09-15 15:05:54) [WARNING ] Unable to interpret mime type for content type '/json'. Defaulting to text/plain.
===============================================================================
All tests passed (10 assertions in 1 test case)

After:

Filters: "custom_content_types"
Randomness seeded to: 3563733199
(2025-09-15 15:05:33) [WARNING ] Unable to interpret mime type for content type 'custom/type'. Defaulting to text/plain.
(2025-09-15 15:05:33) [WARNING ] Unable to interpret mime type for content type 'notarealextension'. Defaulting to text/plain.
(2025-09-15 15:05:33) [WARNING ] Unable to interpret mime type for content type 'image/'. Defaulting to text/plain.
(2025-09-15 15:05:33) [WARNING ] Unable to interpret mime type for content type '/json'. Defaulting to text/plain.
===============================================================================
All tests passed (10 assertions in 1 test case)

test/unittest "simple_response_routing_params":

Outputs are equivalent in aggregate.

Before:

Filters: "simple_response_routing_params"
Randomness seeded to: 3649381328
===============================================================================
All tests passed (14 assertions in 1 test case)

After:

Filters: "simple_response"
Randomness seeded to: 4187677161
===============================================================================
All tests passed (9 assertions in 1 test case)

Filters: "routing_params"
Randomness seeded to: 124073252
===============================================================================
All tests passed (5 assertions in 1 test case)

[gittiver]

please replace globbing by explicit file listing