Migrated the JSON serialization stack from System.Text.Json to Newtonsoft.Json (13.0.3) across the core library, KasaClient.Console, tests, and benchmarks. This avoids extra binding-redirect dependencies that System.Text.Json requires on .NET Framework 4.7.2 and improves reliability on embedded Mono hosts. No public API or behavior changes; validated with a full solution build across net472/net10.0 and live device integration tests against real plugs, bulbs, light strips, and hubs. See CHANGELOG.md for details.