Parameter structs for super::trait_def::PlanVisitor methods whose
SqlPlan variant carries enough fields to exceed clippy’s
too_many_arguments threshold. Each struct bundles one method’s
parameters (minus &mut self) so the trait method itself stays under
the arg-count cap while still exposing every field to implementors.
Executor parity contract for SqlPlan: one abstract method per variant.
Trait method arity mirrors SqlPlan variant field counts and is not a code smell.
Variants whose field count would exceed clippy’s too_many_arguments cap take a
bundled params struct from super::args instead of raw positional arguments.