Migrate to Java 17 and Jackson 3

[gregjotau]

Summary

Implements the next-major direction proposed in #1899:

• make Java 17 the minimum supported runtime and compiler release
• migrate Jackson core/databind usage from com.fasterxml.jackson 2.x to tools.jackson 3.x
• retain com.fasterxml.jackson.core:jackson-annotations 2.x, which Jackson 3 intentionally continues to use
• migrate handwritten serializers, deserializers, mapper configuration, tests, and the v7 generation templates
• reject accidental legacy Jackson 2 core/databind/datatype/module dependencies with Maven Enforcer
• test the supported JDK matrix on 17, 21, and 25

The generator companion is Adyen/adyen-sdk-automation#154. It now keeps OpenAPI Generator 7.11.0 and adds only the import mapping needed by Adyen's existing custom Jersey 3 templates. This avoids coupling the Jackson migration to unrelated output changes from an OpenAPI Generator upgrade.

Compatibility notes

This is intentionally a breaking, next-major change. Applications must run on Java 17 or newer. Jackson 3 exceptions and mapper APIs are used where Jackson 2 types no longer exist; annotations keep their com.fasterxml.jackson.annotation package because that artifact remains shared with Jackson 3.

Regression coverage

Focused Jackson 3 tests now cover:

• rebuilding a mapper after setDateFormat, including preservation of modules and configuration
• visibility of the volatile mapper during concurrent reads and reconfiguration
• generated oneOf deserialization
• UTF-8 byte-array serialization and deserialization round trips

The byte-array serializer now uses UTF-8 explicitly, matching the deserializer and removing platform-default behavior.

Generation reproducibility

• ./gradlew :java:cleanRepo :java:sessionauthentication in the automation companion regenerates a clean library worktree against this branch with OpenAPI Generator 7.11.0.
• ./gradlew :java:services succeeds against the requested OpenAPI schema commit bee086f without any Jackson 2 core/databind imports.
• The full-services run has 13 tracked changes and 21 new generated paths from API snapshot drift already present with 7.11.0. The library's current baseline commit generated only the payment service, so those unrelated service updates are not included here.

Validation

• 622 tests discovered: 618 passed and 4 existing tests skipped
• mvn -Dgpg.skip=true clean verify
• mvn dependency:analyze -DfailOnWarning=true
• focused Jackson 3 regression tests also pass on JDK 25
• ./gradlew :buildSrc:test in the generator companion
• clean downstream ReAI Spring Boot 4 application build using the published compatibility artifact

[gemini-code-assist]

Code Review

This pull request upgrades the project's runtime baseline to Java 17 and migrates the serialization framework from Jackson 2 to Jackson 3, updating imports, exception types, and custom deserializers across all model files. The review feedback identifies opportunities to simplify the JsonMapper configuration using cleaner Jackson 3 builder APIs and highlights a thread-safety issue where a shared static mapper is reassigned concurrently in setDateFormat across multiple packages.

[gregjotau]

Thanks for the review. I addressed the valid mapper visibility concern in 98125da: the generated ObjectMapper reference is now volatile in the template and all current generated copies.

I kept changeDefaultPropertyInclusion(...) because Jackson Databind 3.1.5's MapperBuilder exposes that API but does not expose the suggested serializationInclusion(...) method.