@safe'ty of find and canFind

Change find's tests to validate usability of @safe.
Eliminate the trustedFindRR case by pushing it down a layer in the find stack of functions.
Mark unpredictableSeed as @trusted (@safe is a stretch due to all the casting) so that it can be used in @safe contexts.
Mark canFind's tests to validate usability of @safe (which lead to the unpredictableSeed change)