test: verify sanitizer build configuration - #1716

What does this PR do?

Fixes #1648 by checking what each test runner was actually compiled with.

test-runner --build-config exits before suite or test-cache setup and prints one exact line: sanitized=<0|1> test_seams=<0|1>. scripts/test.sh checks that line immediately after building the runner in its iteration, full, and TSan paths. scripts/msan.sh performs the same check before its suites start. If a stale or misconfigured runner disagrees with the lane, the script now stops before any suite can run with the wrong timing budget.

The patch only changes tests/test_main.c, scripts/test.sh, and scripts/msan.sh. It does not touch the Makefile, workflows, dependencies, or production code.

Current CI

On head e3c0010267e783b4270e0ac7c8ee6332b61aeabb, PR CI has finished: 29 checks passed, 2 failed, 1 skipped. DCO, lint, memory analysis, CodeQL, Linux/macOS tests, diagnostic sanitizers, MSan, LSan, all three TSan lanes, Windows guards, the second Windows shard and shard completeness passed.

The first Windows CLANG64 shard reported 4,106 passed, 1 failed, 12 skipped. The failure is version_cohort_crash_releases_process_lifetime_lease at tests/test_version_cohort.c:950, ASSERT(ready); the aggregate ci-ok consequently failed. This is not a build-config mismatch.

The same named test and assertion also failed in PR #1817's Windows run on 24 August, whose head 87576413 does not contain this PR's build-config probe. The failing test, cohort implementation and subprocess implementation are unchanged from the current base. This establishes a prior occurrence outside this patch; it does not establish the underlying Windows failure mechanism. Native Windows ARM64 remains unverified.

Original implementation checks

• Plain runner: sanitized=0 test_seams=1
• Default and explicit UBSan runners: sanitized=1 test_seams=1
• Empty and whitespace-only SANITIZE paths
• Reused plain build followed by a default sanitized iteration, which failed at the new check before the suite
• Full scripts/test.sh on Linux x86-64
• bash -n scripts/test.sh scripts/msan.sh
• git diff HEAD^ HEAD --check
• Commit signature and DCO checks

Apple Silicon ASan and TSan fail in the sanitizer runtime before main, so they do not provide evidence about this patch. The remote MSan path is also blocked before its build command because the Compose service is pinned to linux/arm64 and the x86-64 builder has no binfmt/QEMU registration. These are historical local-environment limits; current CI coverage and the remaining Windows failure are recorded above.

The original full local lint reached existing diagnostics in unchanged source files; none of the three files in this patch appeared in that output. Current CI lint and memory analysis have passed.

Checklist

• Every commit is signed off (git commit -s): CI requires DCO.
• Required CI is fully green: the first Windows shard and aggregate ci-ok remain red as described above.
• CI lint and memory analysis pass on the current head; historical local baseline limitations are disclosed above.
• New behavior is covered by the test entrypoints and focused positive and stale-build checks.