Miscellaneous Improvements ahead of RePacking

[Sewer56]

This PR contains a few miscellaneous improvements:

• Nx can now pack files greater than 2GiB in size from disk.
  • Streams are still limited to 2GiB. will throw if the limit is breached.
  • This is a breaking change in binary. But not a breaking change in source.
• A tiny refactor of the packing/unpacking steps.
  • Moved some of the packing/unpacking steps to separate files.
  • Added explanations on why each step is necessary and what it achieves.
  • This is to make the code reusable for repacking, and easier to understand.
• Updated Documentation
  • Documentation now includes the previously missing Compression class, since it went from internal to public.
  • Documentation had some minor fixes, e.g. a typo in one code snippet.
  • Added extra notes.