feat: rework download logic with checksums

[Saghen]

Closes #459
Closes #68

Adds checksums to the binary and validates it on every startup (takes 1ms, non-blocking). If the checksums don't match, the binary will be re-downloaded. Should also fix a theoretical issue where a failed download would be marked as "locally built"

@scottmckendry If you get the chance, could you test this on windows/mac? I've got a release with checksums up at https://github.com/Saghen/checksum-test

{
  "saghen/checksum-test",
  version = '*',
  config = function(_, opts)
    require('blink.cmp').setup(opts)
  end
},
{
  'saghen/blink.cmp',
  enabled = false
}

[scottmckendry]

Happy to have a look @Saghen! I should have some time in the next day or so.

Fair warning, I don't have access to a mac and I've since returned the android device I was using for testing to its original owner. I can definitely verify Windows, though 🙂

[Saghen]

I ended up setting up windows last night to play a game so I gave it a test while I was there. Thank you as always though!