Add --test_parallel to reduce CTest concurrency for ASan builds

[tianleiwu]

Description

The windows_x64_asan / build_x64 CI pipeline has been failing with OOM (out-of-memory) because ASan-instrumented test binaries consume significantly more memory than normal builds, and CTest was running them at full CPU-count parallelism.

This PR adds a --test_parallel argument to build.py that allows CTest concurrency to be configured independently from the build parallelism (--parallel). It then uses --test_parallel 4 in the Windows x64 ASan workflow to cap test execution to 4 parallel jobs, preventing OOM while keeping build parallelism at full speed.

Motivation and Context

• ASan instrumentation inflates per-process memory usage by ~2-3x.
• The existing --parallel flag controls both MSBuild and CTest concurrency together; there was no way to keep fast parallel builds while limiting test concurrency.
• The CI runner has limited memory, and running all tests in parallel under ASan exceeded available RAM.

Changes

File	Change
tools/ci_build/build_args.py	Add --test_parallel argument (default: None, falls back to --parallel)
tools/ci_build/build.py	Add number_of_test_parallel_jobs() helper; use it for CTest --parallel; validate negative values
.github/workflows/windows_build_x64_asan.yml	Pass --test_parallel 4 to cap ASan test concurrency

Testing

• python -m py_compile tools/ci_build/build.py tools/ci_build/build_args.py — passes
• python tools/ci_build/build.py --help shows the new --test_parallel option
• git diff --check — no whitespace issues
• When --test_parallel is omitted, behavior is unchanged (falls back to --parallel value)