Fix hashing overflow issues (#86)

[FlickerSoul]

This PR fixes overflow errors during hashing persistent data structures.

[Julian]

Nice! Any chance you also might take a stab at the suggestion to run with --profile=dev in CI? I'm not 100% sure what it does (so a good first step is probably double checking) but if we don't add it, it's obviously likely we could accidentally add some other thing which trips it.

[FlickerSoul]

It looks like the arguments are passed to maturin and then to cargo during building rpds. See here and here. The dev profile enables the overflow check and that's why we see the errors in the issue. It could be helpful in terms of debugging and producing extra information, I think?

[Julian]

From that page it would seem like we should run with --profile=test, which implies dev.

[FlickerSoul]

Yes I think test would make more sense. I can modify the CI to do that :)

[Julian]

@FlickerSoul let me know if you're still up for making the CI change! (Thanks again for your work so far)