throttle cpu and network conditions in puppeteer using a cdpsession for performance testing

Steps

1. create a CDP session with await page.target().createCDPSession() (or the higher-level page.createCDPSession() depending on the installed version)
2. send client.send('Network.enable') followed by client.send('Network.emulateNetworkConditions', { offline: false, downloadThroughput, uploadThroughput, latency }) to simulate a constrained connection such as slow 3G
3. send client.send('Emulation.setCPUThrottlingRate', { rate: 4 }) to simulate a CPU roughly four times slower than the test machine
4. run the page interaction or navigation under test and measure timing metrics (e.g. via the Performance API or Lighthouse-style metrics) under the throttled conditions
5. reset throttling (rate: 1, and network conditions back to unrestricted) at the end of the test so it does not leak into subsequent tests sharing the same page or context