Stateful Serdes, System.Text.Json UnionEncoder, STJ autoUnion mode

NOTE: Unlisted in favor of 2.3.1, which has a critical fix for autoUnion mode's handling of option and list types.

Added

• SystemTextJson.UnionOrTypeSafeEnumConverterFactory: Global converter that automatically applies a TypeSafeEnumConverter to all Discriminated Unions that support it, and UnionConverter to all others #69
• SystemTextJson.Options(autoUnion = true): Automated wireup of UnionOrTypeSafeEnumConverterFactory #69
• SystemTextJson.UnionConverter: Port of NewtonsoftJson equivalent started in #43 #59 🙏 @NickDarvey

Changed

• Serdes: Changed Serdes to be stateful, requiring a specific set of Options/Settings that are always applied consistently #70
• Serdes.DefaultSettings: Updated README.md ASP.NET integration advice to reflect minor knock-on effect #70
• SystemTextJson: Target System.Text.Json v 6.0.1, TypeShape v 9.0.0 #68

See CHANGELOG