[ML] Fix test parallelism bug and pre-compile tests to prevent OOM

Fix $(TEST_PARALLEL) -> ${TEST_PARALLEL} typo in docker_entrypoint.sh.
The command substitution syntax caused bash to try to execute a command
called TEST_PARALLEL (which doesn't exist), resulting in an empty string
and cmake interpreting bare -j as unlimited parallelism. This led to OOM
kills during test compilation on CI agents.

Also pre-compile test executables via build_tests target before running
test_all_parallel, ensuring no compilation happens concurrently with
test execution.

Made-with: Cursor

Author: edsavage

dev-tools/docker/docker_entrypoint.sh

@@ -79,6 +79,7 @@ if [ "x$1" = "x--test" ] ; then
         TEST_PARALLEL=$(( (NCPUS + 1) / 2 ))
     fi
     echo "Test parallelism: nproc=${NCPUS}, TEST_PARALLEL=${TEST_PARALLEL} (cmake --build -j ${TEST_PARALLEL})"
-    cmake --build cmake-build-docker ${CMAKE_VERBOSE} -j $(TEST_PARALLEL) -t test_all_parallel || echo failed > build/test_status.txt
+    cmake --build cmake-build-docker ${CMAKE_VERBOSE} -j ${TEST_PARALLEL} -t build_tests
+    cmake --build cmake-build-docker ${CMAKE_VERBOSE} -j ${TEST_PARALLEL} -t test_all_parallel || echo failed > build/test_status.txt
 fi