Catch2 supports dynamically defining test cases, and also supports dynamically loading them into CTest. Instead of a monolithinc "test_unified_format_spec" test case from a single test executable, we can use `registerTestCase()` in Catch2 to dynamically add test cases for each test defined in the test spec files.

Additionally, the catch_discover_tests() CMake command (from Catch.cmake) can be used to register each Catch2 test case as a test in CTest. From this, CTest can track and execute each Catch2 test case individually, including in parallel, respecting `--rerun-failed`, detecting skips, etc.