test: wait for debugger pause state on startup

[trivikr]

This updates the debugger test helper to wait for the debugger CLI
to reach a paused state instead of depending only on the printed
initial break banner.

The helper now probes with list() and retries while the CLI reports
that execution is not paused. Each probe wait uses the remaining
timeout budget so the overall startup wait still respects the helper
timeout.

Refs: https://github.com/nodejs/node/actions/runs/27683841143/job/81877654047

Error log

Path: parallel/test-debugger-exec-scope
Error: --- stderr ---
/Users/runner/work/node/node/node/test/common/debugger.js:92
        const timeoutErr = new Error(`Timeout (${TIMEOUT}) while waiting for ${pattern}`);
                           ^

Error: Timeout (15000) while waiting for /break (?:on start )?in/i
    at /Users/runner/work/node/node/node/test/common/debugger.js:92:28
    at new Promise (<anonymous>)
    at Object.waitFor (/Users/runner/work/node/node/node/test/common/debugger.js:67:14)
    at Object.waitForInitialBreak (/Users/runner/work/node/node/node/test/common/debugger.js:116:18)
    at file:///Users/runner/work/node/node/node/test/parallel/test-debugger-exec-scope.mjs:13:13
    at ModuleJob.run (node:internal/modules/esm/module_job:447:25)
    at async node:internal/modules/esm/loader:646:26
    at async asyncRunEntryPointWithESMLoader (node:internal/modules/run_main:101:5) {
  output: '\n' +
    '< Debugger listening on ws://127.0.0.1:55107/b43be8c5-442d-49a8-80ce-1ff2d58af386\n' +
    '< For help, see: https://nodejs.org/learn/getting-started/debugging\n' +
    '< \n' +
    'connecting to 127.0.0.1:55107 ...\n' +
    '< Debugger attached.\n' +
    '< \n' +
    '\n' +
    ' ok\n' +
    '\n' +
    'debug> '
}

---

Assisted-by: openai:gpt-5.5