core: add helper macros for deserialization

A helper function would seem more natural, but there are two reasons why a
macro is needed:
- many bool fields are bitfields, so we can't take a pointer, and using a macro
  allows us to avoid taking a pointer.
- we have a few diffent types (bool, uint64_t, FreezerState), and we can have
  type safety without specifying the type by using the macro.

This also makes the error messages more informative: they print the exact field
identifier that failed, which is more useful for debugging than a description.