invoked when an error is leaving the DBIC internals to be handled by
the caller (n.b. https://github.com/PerlDancer/Dancer2/issues/1125)
(also fixes the previously rejected RT#63874)
+ - Overrides of ResultSourceProxy-provided methods are no longer skipped
+ silently: a one-per-callsite warning is issued any time this tricky
+ situation is encoutered https://is.gd/dbic_rsrcproxy_methodattr
- $result->related_resultset() no longer passes extra arguments to
an underlying search_rs(), as by design these arguments would be
used only on the first call to ->related_resultset(), and ignored