Rearrange tests & fix CI (#4596)

* Rearrange tests into unit/integration/challenge categories

* Fix linting + `tests.challenges` imports

* Fix obscured duplicate test in test_url_validation.py

* Move VCR conftest to tests.vcr

* Specify tests to run & their order (unit -> integration -> challenges) in CI

* Fail Docker CI when tests fail

* Fix import & linting errors in tests

* Fix `get_text_summary`

* Fix linting errors

* Clean up pytest args in CI

* Remove bogus tests from GoCodeo

tests/challenges/debug_code/data/two_sum.py

@@ -0,0 +1,19 @@
+# mypy: ignore-errors
+from typing import List, Optional
+
+
+def two_sum(nums: List, target: int) -> Optional[int]:
+    seen = {}
+    for i, num in enumerate(nums):
+        complement = target - num
+        if complement in seen:
+            return [seen[complement], i]
+        seen[num] = i
+    return None
+
+
+# Example usage:
+nums = [2, 7, 11, 15]
+target = 9
+result = two_sum(nums, target)
+print(result)  # Output: [0, 1]