This reverts commit f1af0cae674f7dea29d460c5b630a58c59c7dcab.
Motivation for revert:
At least 1 user has reported depending on the current `cache`
feature, and implementing it manually (i.e. outside of Nippy) can
be non-trivial.
Rather than risk breaking folks, I'll take some more time to
consider alternatives. There's no urgency on this.
This commit is BREAKING for those still actively using `nippy/cache`.
Data previously frozen using `nippy/cache` can still be thawed, though
support for thawing may also be removed in a future Nippy version.
Motivation for removal:
This cache feature (marked as experimental) was always a bit dubious.
The use cases were very limited, and the complexity quite significant.
I don't believe that the feature has ever had much (any?) public
adoption, so I'm removing it here.
PLEASE LET ME KNOW if this removal negatively impacts you.
