The socket_transport_int integration test intermittently failed (observed on
ARM64, reproducible deterministically on x64 Debug) with a nonzero exit code
even though all tests passed. ctest derives the exit code from the VLD leak
count delta. The leaked block traced to a one time 256 byte loader allocation
made when Winsock lazily loads a namespace provider DLL on the first
getaddrinfo call (during the first test). VLD's end of process report confirms
no real leak; the block is just outstanding when ctest samples the count, and
whether it is counted is timing dependent.

Switch the test to a custom main that warms up Winsock name resolution before
RUN_TEST_SUITE, so the one time provider DLL allocation is folded into the leak
baseline that ctest captures at the start of the run, netting the delta to
zero. WSACleanup is called after the warm up so Winsock per startup caches are
freed. Add the standard main_cpp_unittest.cpp for the CppUnitTest DLL variant
that the custom main build produces.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>