CT: Improve memory testing

[zepumph]

@jonathanolson and I have found while working on https://github.com/phetsims/special-ops/issues/234 that ?memoryLimit=43728 is not behaving very well when tested on CT. Instead, we should develop our own, custom test that emphasizes memory improvements. Here are some ideas:

• page.collectGarbage() puppeteer/puppeteer#1394 points to https://pptr.dev/api/puppeteer.page.queryobjects as a way to "force garbage collection". THat may be nice to do before we ask for the heap size. Note I didn't see this feature for playwright's Page class.
• Use https://pptr.dev/api/puppeteer.page.queryobjects to query Scenery of PhET classes like Node or Property or Vector2, to see if those are leaking.
• Likely we should use a combo of both of those, by toggling fuzzing and resetting screens before capturing this data.
• Maybe something else!?