perf(cli): Extract next-test constants to avoid eager loading
Move SUPPORTED_TEST_RUNNERS_LIST constant to a separate lightweight
file to prevent loading heavy next-test.ts dependencies (loadConfig,
verifyTypeScriptSetup, etc.) when the CLI starts.
This reduces CLI startup time from ~38ms to ~18ms (~53% faster) by
avoiding transitive module loading at startup.
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
