fix: [JAVA][SPRING] Nullaways warn with JSpecify => add missing annotation to parameter of method toIndentedString

[wing328]

based on #22599 with resolved merge conflicts

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Summary by cubic

Add @nullable to the toIndentedString parameter in generated Java Spring models to align with nullability handling and silence static analysis warnings. Updated tests and regenerated samples; no runtime behavior change.

• Bug Fixes
  • Add {{>nullableAnnotation}} to toIndentedString parameter in JavaSpring/pojo.mustache.
  • Extend SpringCodegenTest to assert the annotated signature.
  • Regenerate affected Spring samples (cloud, http-interface, reactive) to include the change.

^{Written for commit 20383b7. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 1198 files

Note: This PR contains a large number of files. cubic only reviews up to 75 files per PR, so some files may not have been reviewed.

[typat]

Hi there! I'm trying to implement JSpecify using this new logic. Do you have a sample configuration for how to trigger the @Nullable annotations on fields marked nullable: true without using the JsonNullable wrapper?

I've tried setting openApiNullable: false and mapping Nullable to org.jspecify.annotations.Nullable in importMappings, but I'm having trouble getting the annotation to render in the generated Java models.

edit: NVM I realized I had useNullable set to true. There seems to be a specific set of values in order to produce Null annotations, which is fine. I just didnt have it. Thank you!