feat(gallery): expand code generation examples with individual annotation options

- Add one example per annotation option for each code generator
- Add combined 'All' examples showing all annotations together
- For C#: show Avro, System.Text.Json, Newtonsoft, protobuf-net, XML, MessagePack, CBOR separately
- For C# combined: prefer System.Text.Json over Newtonsoft
- Python: Avro and dataclasses-json examples
- Java: Avro and Jackson examples
- TypeScript: Avro and TypedJSON examples
- Rust/Go/C++: Avro and JSON examples

Note: Gallery pages will be regenerated by CI

Author: Clemens Vasters