lisa.utils: Memoize SimpleHash.__hash__ perf
lisa.utils: Memoize SimpleHash.__hash__ perf

Memoize the hash, as the objects are necessarily immmutable and the hash
computation can be quite expensive.

ARM-software/lisa,credp/lisa,ARM-software/lisa,credp/lisa,ARM-software/lisa,ARM-software/lisa,credp/lisa,credp/lisa