Preserve list-valued properties in catch_discover_tests

Description

catch_discover_tests(tests PROPERTIES ENVIRONMENT "FIRST=one;SECOND=two") currently passes only the first environment variable to discovered tests. Argument parsing and forwarding flatten the list-valued property, losing the property/value boundary.

Preserve argument boundaries in the public parser and carry the encoded properties as one argument into test registration. Keep the existing list semantics for the executor so multi-argument emulators continue to work.

The integration regression covers PRE_TEST and POST_BUILD, verifies the CTest properties, and runs a real testcase that reads all environment variables. It includes a literal semicolon, an empty environment value, scalar properties, and a multi-argument emulator. Both modes fail on the unchanged base and pass with this change.

Validation on Linux/GCC 13.3/CMake 3.28.3: complete all-tests build and all 157 CTest checks pass, including the existing name/tag/TEST_LIST and DL_PATHS checks. The changed fixture passes C++14 syntax and formatting checks; the Python verifier passes syntax checking. Generated amalgamated files were rebuilt locally and are excluded from the commit.

Prepared with OpenAI Codex assistance; the reported failure was reproduced and the submitted source was tested locally.

GitHub Issues

Closes #2424.