Benchmark and improve object creation

[iboB]

Benchmarks of https://github.com/iboB/huse show unexpectedly long time spent in object creation where the type cache query is practically a hit 100% of the time. It seems that it takes 90us to create an object in the json-parse benchmark there.

We should benchmark (and likely optimize) object creation.

• Check with a known type: mutate_to
• Check by mutating to a hit: mutate leading to a known type