fix: unused-template warnings (#6156) * fix: remove `static` from `type_id` * Add -Wunused-template for Clang 18 * fix: remove `static` from `type_has_shared_from_this` * Remove unreachable overload. --------- Co-authored-by: Ralf W. Grosse-Kunstleve <rgrossekunst@nvidia.com>