Parsing nested groups

[unlessgames]

As mentioned on the forum, parsing expressions like [ [ [ [ ] ] ] ] takes a long time for pest with the current rules.

I found this issue on the pest github that seems relevant.

Clearly the rules inside groups have some similar retrying that was mentioned on the issue as for example a stack can have a split or a section inside while a group can have a stack, split or section but I'm not sure how we could optimize this exactly and profiling might be a good idea before trying to do anything here.

[emuell]

This seems to be s general Pest issue after all.

See also martinohmann/hcl-rs#82

Let me know if I can help setting up some benchmarks or writing a guide on how to profile this. I can try taking care of this issue too next week if you don't have time for that.