Add very simple unit tests as a starting point for the new parsing functions in `util/parsing.py`.
Code is based on `common.DataSizeToUint64` in Composer, with a modification to allow `unlimited` so that the result is compatible with `fscache.MaximumSizeType`. [1] f4aed3e6e2/internal/common/helpers.go (L46)
f4aed3e6e2/internal/common/helpers.go (L46)