Up to this point, we've had to rely on making `Strategy` constants
private to ensure that the only available constants are strategies.
With the current setup, the existence of a constant that's not a
strategy would break `Strategy#strategies` and
`Livecheck#livecheck_strategy_names`.
Instead, we can achieve the same goal by skipping over constants
that aren't a class. Other than saving us from having to make these
constants private, this is necessary to be able to create a
`Strategy` constant that can be used in all strategies.
The simple approach here caches all header or body content from
responses, so memory usage continually grows with each fetch. This
becomes more of a notable issue with long livecheck runs (e.g.,
`--tap homebrew/core`).
Instead, we should only cache the header/body for URLs that we know
will be fetched more than once in a given run. Being able to
determine which URLs will be fetched more than once requires
structural changes within livecheck strategies, so this will take a
bit of work to implement.
I've been working on this off and on and I'll introduce a more
sophisticated method of livecheck-wide caching in a later PR. In the
interim time, it's best to remove this caching behavior until I've
finished working on an approach that provides benefits (reducing
duplicate fetches) while minimizing detriments (increased memory
usage).
