perf: use cow-utils instead

[heygsc]

We can improve performance by using cow_utils, and automatically check in clippy.

We have done similar work before, and if necessary and possible, I would like to provide pr for gosub.

Related issue:
#752
oxc-project/oxc#5586

[jaytaph]

Hi!. This is something we really want as well.. The html parser for instance is written at a time there wasn't too much experience with Rust, so there is a lot of cloning and copying of data which probably shouldn't happen. @Sharktheone your thoughts?

[Sharktheone]

I think this is something we can do. Maybe we can save this as a more general string optimization. For example, in some places, we should replace the std String with some SmallString variant. Or more specifically, in the HTML parser we are currently not sharing the namespace. And I think we also store the source file name, that should also be shared.