fix(benchmarks): keep config imports safe for workflow sandboxes

[ayush-or]

TL;DR

Importing the benchmark config crashes Temporal workflow initialization because it also initializes the Effect model service, which writes Error.stackTraceLimit after Temporal freezes globals. Keep the config import free of that service initialization.

What changed?

• Move the existing pure stripVariantSuffix helper into the constants module and import it directly from the benchmark config.
• Re-export the helper from the model module so existing callers keep working.
• Add an isolated subprocess regression test that imports the real config with frozen Error.

How to test

Validated commit e1d6728d9dc88f7da5405085b98fae481642c94c with an isolated install from the committed lockfile:

• bun run format:check: passed.
• bun run check: passed, with existing warnings outside the changed files.
• bun run typecheck: passed.
• bun test: 1,562 passed, 0 failed.
• bun run build: passed.
• Regression check: temporarily restoring the original config import makes the new test fail with Attempted to assign to readonly property; restoring the fix makes it pass. The working tree is clean.

CI validation passed. The original failure is captured by the downstream production Temporal bundle test. The full downstream integration test must be rerun after syncing the merged fix.

Reviewer focus

The helper behavior and existing model-module export are unchanged. This PR is the upstream prerequisite for the harness sync in openrouter-web #47047. The monorepo subtree accepts merged upstream main snapshots only; no vendored source changes are included there.