The `hyperlight-guest` crate exports more items than it should

The doc.rs page has a list of all the items exported by `hyperlight-guest`: https://docs.rs/hyperlight-guest/latest/hyperlight_guest/all.html

There are items that look like they should not be exported, to name a few:
* `print::_putchar`
* `gdt::load_gdt`
* `memory::*`

These items are currently part of the public API, meaning that downstream consumers could start relying on them.
IMHO, we should trim down the public API, and only add things as needed.