Fully separate parent and child resultsource metadata

Fully separate parent and child resultsource metadata

Ensure that all attributes are shallow-copied on "clone". Currently this
means that the following are *NO LONGER* shared between rsrc clones:

_unique_constraints
_primaries
source_info

This seems just as cocky and reckless as the clusterfuck in 4006691d/RT#107462
and it most likely will have the same invisible-yet-dire consequences for
various downstreams. However there is a plan in place several commits ahead
allowing sidestepping the impossibility to debug a potential fallout.