Find encoding/json usage for the v2 migration

Inventory every encoding/json (v1) touchpoint that an encoding/json/v2 migration must address: the import, package functions, Encoder/Decoder and other type methods (resolved through the type system, so receivers reached via variables, parameters, or fields are all found), exported types, [N]byte/time.Duration struct fields, omitempty and ,string tags, and custom MarshalJSON/UnmarshalJSON implementations. Findings populate a data table categorized as import, rewrite, review, or modernize. This recipe reports only and does not modify code.