Resolvers don't support caching

[victor-paltz]

In OmeaConf it is possible to cache the resolver results (by default a custom resolver is called on every access).
Caching is required when using random functions to ensure the same value is always returned (ex: for a random search).
This feature is not available in fromconfig.

OmegaConf doc: https://omegaconf.readthedocs.io/en/2.3_branch/custom_resolvers.html
Code to change:

fromconfig/fromconfig/parser/omega.py

Line 73 in dbad702

OmegaConf.register_new_resolver(name, resolver)