[Bug]: Add top level `endTime` when using --json reporter

[pdehaan]

Version

29.7.0

Steps to reproduce

1. Add basic sum.js and sum.test.js getting started.
2. jest --json --outputFile=jest.json --testLocationInResults --verbose
3. Inspect the generated jest.json report.

Expected behavior

Top level startTime and endTime in the generated results file. We're trying to build a dashboard for Jest and Playwright and build times so we can track them for the past n days, but I'm only seeing the total test time reported in STDOUT and not in the outputFile, which makes it tricky.

Actual behavior

startTime but no endTime (so we can calculate test execution duration)

// jest.json
{
  "numFailedTestSuites": 0,
  "numFailedTests": 0,
  "numPassedTestSuites": 1,
  "numPassedTests": 1,
  "numPendingTestSuites": 0,
  "numPendingTests": 0,
  "numRuntimeErrorTestSuites": 0,
  "numTodoTests": 0,
  "numTotalTestSuites": 1,
  "numTotalTests": 1,
  "openHandles": [],
  "snapshot": { ... },
  "startTime": 1717304192877,
  "success": true,
  "testResults": [ ... ],
  "wasInterrupted": false
}

Versus STDOUT's output:

jest --json --outputFile=jest.json --testLocationInResults --verbose

 PASS  ./sum.test.js
  ✓ adds 1 + 2 to equal 3 (1 ms)

Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        0.1 s, estimated 1 s
Ran all test suites.
Test results written to: jest.json

Additional context

No response

Environment

System:
    OS: macOS 14.5
    CPU: (10) arm64 Apple M1 Max
  Binaries:
    Node: 22.2.0 - ~/.nvm/versions/node/v22.2.0/bin/node
    npm: 10.7.0 - ~/.nvm/versions/node/v22.2.0/bin/npm
  npmPackages:
    jest: ^29.7.0 => 29.7.0