Add testcases for concept constrained overload by arity, member operator
overloads, structural partial specialization with a requires-clause, and
the concept only function template redefinition that trips warning 302
(errors/cpp_concept_redefinition). Document existing support for
constrained class templates and member function templates of plain
classes, and the limitations around constraint subsumption: same-
signature templates differing only by requires-clause are dropped, and
concept only "partial specializations" are not selected.
Assisted-by: Claude Code (Opus 4.7)
William S Fulton