While this works, it's less efficient than alternatives. If the method
accepts an options hash, the `**` can be dropped, avoiding a hash
allocation. If the method accepts keywords, `**hash, **other_hash` can
be used.
However, in the cases where we are using these constructions, one of
the hashes is a literal hash, so these constructions result in
2-3 hash allocations:
* 1 for the literal hash
* 1 for the Hash#merge
* 1 if the keyword splat is converted to a positional hash
using `**hash, kw: value` reduces this to a single hash allocation,
in addition to being simpler.
For the create_cache_entry change in the specs, use an anonymous keyword
splat parameter. This is done for simplicity, it doesn't save
allocations in this case (as all callers are providing literal keywords).
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