8.3.1: stream application/jsonl, and refuse the deprecated application/stream+json

[joseegman-idoneea]

Summary

Follow-up to #472: this commit reached its branch after it was merged, so 8.3.0 shipped without it.

application/jsonl streams like application/x-ndjson

OpenAPI 3.2 names JSON Lines as a sequential media type, and it is the same format as NDJSON. It now takes the same generated code:

• Spring MVC servers get the endpoint/method pair, and NdjsonSupport.stream(...) sends the media type the contract declares instead of always application/x-ndjson.
• WebFlux servers and reactive @HttpExchange interfaces use Flux<T>.
• ApiWebClient registers application/jsonl in its Jackson codecs and as a streaming type of the encoder, so a Flux body is sent line by line, not as a JSON array.

Spring's own codecs stream application/x-ndjson only. For JSON Lines, a WebFlux server, or a reactive @HttpExchange backed by the application's WebClient.Builder, needs a CodecCustomizer. The README shows it for Boot 4 and for Boot 2/3.

application/stream+json fails the generation

8.3.0 treated it as a stream, but it is deprecated. Spring Framework 7 no longer streams it, and ApiWebClient's codecs, which list JSON and NDJSON only, would not read it. The generation now fails with a message asking for application/x-ndjson or application/jsonl.

Test plan

• testNdjsonStreaming gains a JSON Lines response and body (/items/lines) in every variant; new error test for application/stream+json
• Changed assets reviewed: the new operations, the media type argument of NdjsonSupport.stream, and the ApiWebClient (Boot 4) codecs
• Engine: 256 tests green, checkstyle green; Maven plugin ITs green; Gradle test integrationTest green (JDK 21)
• Runtime check outside the repo against Spring Boot 2.7.18, 3.5.8 and 4.0.8, over real HTTP; 23 tests green:
  • the MVC server sends Content-Type: application/jsonl lines and reads a JSON Lines body;
  • the generated WebClient client (2.7) receives and sends JSON Lines;
  • reactive @HttpExchange (4.0) does too with the README's CodecCustomizer, and fails with UnsupportedMediaTypeException without it.
• Version bumped to 8.3.1 in all 5 places

🤖 Generated with Claude Code

[codacy-production]

Up to standards ✅

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