implement Sys_GetFrame in C and add notes about future optimizations

[Vizonex]

What do these changes do?

We need to start chipping away at known bottlenecks otherwise rsloop is going to keep racking up benchmark points. For now I'll stick to improving winloop and let it be a bag of ideas for uvloop to try and implement.

Are there changes in behavior for the user?

Nope. Other than needed performance changes, nothing new, expect better performance.

Is it a substantial burden for the maintainers to support this?

Added Notes about possible improvements,

• c-ares is under consideration
• Other items have been just marked as being improvable in C or in other ways, we need to limit the amount of times the interpreter and compiled code pass each other if we really want to make due on the future ahead.

Related issue number

Checklist

• I think the code is well written
• Unit tests for the changes exist
• Documentation reflects the changes

[Vizonex]

I think winloop is going back to being uvloop's bag of ideas to try.