[BUG][KOTLIN] Jackson3 option does not discover modules like Jackson2 does

[pkubowicz]

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

Serializer generated with useJackson3: true is different from the one generated for Jackson 2: it does not load modules.

Any third-party Jackson 3 module on the classpath is silently ignored. Concrete case: org.openapitools:jackson-databind-nullable:0.2.11 ships META-INF/services/tools.jackson.databind.JacksonModule → JsonNullableJackson3Module, which never gets registered, so JsonNullable fields serialize/deserialize wrongly

openapi-generator version

7.25.0; not a regression, rather a bug in a new feature added in #24709

OpenAPI declaration file content or url

N/A (the bug is in the infrastructure code, not in models)

Generation Details

eneratorName: kotlin
  configOptions: 
    library: jvm-spring-restclient
    serializationLibrary: jackson
    useSpringBoot3: true
    useSpringBoot4: true
    useJackson3: true

Steps to reproduce

Open <pkg>/infrastructure/Serializer.kt

Actual:

 val jacksonObjectMapper: JsonMapper = jsonMapper {
      addModule(kotlinModule())
      ...
  }

Expected: parity with the Jackson 2 output, which is generated from the same template with
useJackson3: false

 val jacksonObjectMapper: ObjectMapper = jacksonObjectMapper()
      .findAndRegisterModules()
      ...

Related issues/PRs

#24709

Suggest a fix

Change kotlin-client/jvm-common/infrastructure/Serializer.kt.mustache; add findAndAddModules() as the first line of the {{#useJackson3}} jsonMapper { … } block.