commander 15.0.0: Prevent process signal event listener leaks when repeatedly parsing git-style executable subcommands.

# Notes

### What `search_known_solution` answered
The `search_known_solution` call returned no exact matches for commander, only unrelated samples covering CSV resource handling and OpenTelemetry SDK behaviors.

### What a model would have written instead
A typical model or developer expects that invoking a subcommand with Commander's executable runner cleans up all process-level event listeners once the spawned child process exits, leaving the global `process` object in its original state.

### How the wrong version fails
It silently leaks event listeners on the global `process` object for `SIGINT`, `SIGTERM`, `SIGUSR1`, `SIGUSR2`, and `SIGHUP` signals during each subcommand execution, retaining references to `ChildProcess` instances in memory, preventing garbage collection, and eventually triggering a `MaxListenersExceededWarning`.

{"case":{"believed":"Spawning git-style executable subcommands with Commander cleans up all process-level event listeners once the subcommand process exits.","caseId":"case:sha256:647aee2c1db84f82f2ec91ac1f86c0fbba93519da5601a566b1c8eb5f3cf800f","contract":["Spawning executable subcommands in commander registers signal event listeners on the global process object that are never unregistered upon process termination, accumulating memory leaks on subsequent command invocations."],"goal":"Prevent process signal event listener leaks when repeatedly parsing git-style executable subcommands.","kind":"HOW","packages":["pkg:npm/commander@15.0.0"],"schemaVersion":1,"symbols":["Command.prototype.parse","Command.prototype.exitOverride"]},"contractCommand":["node","test/contract.mjs"],"environment":{"arch":"x64","ecosystem":"npm","executionContext":"node","language":"node","os":"linux","packageManager":"npm","runtime":"node","schemaVersion":1},"license":"MIT-0","packages":["pkg:npm/commander@15.0.0"],"schemaVersion":1,"symbols":["Command.prototype.parse","Command.prototype.exitOverride"],"verifierAdapter":"node-typescript@1"}

{
  "name": "npm-commander-sample",
  "version": "1.0.0",
  "lockfileVersion": 3,
  "requires": true,
  "packages": {
    "": {
      "name": "npm-commander-sample",
      "version": "1.0.0",
      "dependencies": {
        "commander": "^15.0.0"
      }
    },
    "node_modules/commander": {
      "version": "15.0.0",
      "resolved": "https://registry.npmjs.org/commander/-/commander-15.0.0.tgz",
      "integrity": "sha512-z67u4ZhzCL/Tydu1lJARtEZYWbWaN7oYLHbsuzocr6y4N6WZAagG3RQ4FW61V1/0+jImpj293XfrcYnd1qxtPg==",
      "license": "MIT",
      "engines": {
        "node": ">=22.12.0"
      }
    }
  }
}

{
  "name": "npm-commander-sample",
  "version": "1.0.0",
  "type": "module",
  "dependencies": {
    "commander": "^15.0.0"
  }
}

import { Command } from 'commander';
import assert from 'assert';

async function run() {
  const program = new Command();
  program
    .name('mycli')
    .command('sub', 'run subcommand');

  const beforeCount = process.listenerCount('SIGINT');

  // First run
  await new Promise((resolve) => {
    program.exitOverride((err) => {
      resolve();
    });
    program.parse(['node', './test/contract.mjs', 'sub']);
  });

  const countAfter1 = process.listenerCount('SIGINT');
  assert.strictEqual(countAfter1, beforeCount + 1, 'Expected exactly 1 new SIGINT listener after the first run');

  // Second run
  await new Promise((resolve) => {
    program.exitOverride((err) => {
      resolve();
    });
    program.parse(['node', './test/contract.mjs', 'sub']);
  });

  const countAfter2 = process.listenerCount('SIGINT');
  assert.strictEqual(countAfter2, beforeCount + 2, 'Expected exactly 2 new SIGINT listeners after the second run');

  console.log('Contract verified: process signal event listeners leaked and accumulated.');
}

run().catch((err) => {
  console.error(err);
  process.exit(1);
});

process.exit(0);