Hey! Thank you for this library! It is very promising and I put a lot of hope into it, as JSDOM is super slow 😄

I was attempting to use it my project a while ago, but there were some issues that were blocking me from migrating from JSDOM. I noticed today your recent releases and decided to give it a try once again.

While most of the issues I have seen are fixed, I noticed that the performance is much worse after upgrading to any version >= 7.0.0. It's hard to make a reproducible example, but I had a test, quite heave one, that in the version 6.x of happy-dom was running in a 1-2 seconds. However, after updating to recent version I see it now taking around 10 seconds 🤯

The issue seems to be related to some of the new code added for better CSS support. I took some CPU snapshots of the same test running on different happy-dom versions.
v6.x:

v7.4.0:

On the second screenshot, most of top items (matchesClass, SeelctorItem, matches, etc...) are coming from happy-dom.

I tried looking at the code for this, but would need to spend much more time to get familiar myself with it, so I decided to first let you know. Do you think there is a chance to improve performance here?
As a temporary solution, I was thinking maybe there would be possibility to skip those CSS changes that are coming from v7.0.0 by setting some flag or something. In most tests I don't need full CSS support (and I assume it might be the same for most cases in general), so enabling it only when needed seems like a acceptable workaround. If it is possible to even add this as a config.

Thank you for help and, again, for your work on this great library! :) Please let me know if you'd need any more details from me.