Sapphire 14 24 ss 1013 deep freeze and deep merge

@tony-spataro-rs added HashTools.deep_freeze! and .deep_merge
the latter differs from deep_merge! because it clones before merging

Object#dup and Object#clone vary in two ways:

1. clone preserves frozen state; dup does not
2. clone copies eigenclass methods onto the new object; dup does not

Wouldn't it be cleaner for us to define deep_dup since we are shooting for semantics that're very similar to dup?