cached_property for file data

[federicazanca]

          One other minor thing: depending on how big the file is and whether the file is liable to change, you may want to make this or `read_yaml` a [`cached_property`](https://docs.python.org/3/library/functools.html#functools.cached_property) to reduce file-opens, but not important.

Originally posted by @oerc0122 in #104 (comment)