Nullability annotations, JavaDoc, refactorings

[afranken]

Description

• Cleanup JavaDoc
  • The API doc and function signatures describe what the functions do, let's describe what they do differently from what is described in the API instead of stating the obvious.
• Implement Delete ObjectTagging
• Add JSpecify Nullability annotations.
• Migrate all Unit tests to Kotlin.

Related Issue

N/A

Tasks

• I have signed the CLA.
• I have written tests and verified that they fail without my change.

[Copilot]

Pull Request Overview

This PR cleans up JavaDoc formatting, adds JSpecify @nullable annotations for improved nullability handling, and refactors several API methods and unit tests (including migrating tests to Kotlin).

• Improved JavaDocs with more concise API references
• Added JSpecify nullability annotations and removed Spring-specific annotations
• Refactored tests to utilize Kotlin naming conventions and updated the build configuration

Reviewed Changes

Copilot reviewed 81 out of 81 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
server/src/main/java/com/adobe/testing/s3mock/dto/*	Added @nullable annotations in enum fromValue methods
server/src/main/java/com/adobe/testing/s3mock/ObjectController.java	Updated JavaDocs and added @nullable to request parameters
server/src/main/java/com/adobe/testing/s3mock/MultipartController.java	Refactored test method names and updated tagging tests
server/src/main/java/com/adobe/testing/s3mock/BucketController.java	Updated JavaDocs and modified region resolution logic
pom.xml and server/pom.xml	Added jspecify dependency and configuration updates
integration-tests/...ObjectTaggingIT.kt	Updated integration tests with Kotlin idioms
README.md and CHANGELOG.md	Updated documentation per new API changes

Comments suppressed due to low confidence (1)

server/src/main/java/com/adobe/testing/s3mock/BucketController.java:373

• Removing the fallback to 'region.toString()' may lead to a null value for bucketRegion if bucketMetadata.bucketRegion() is null. Consider restoring the fallback to ensure LocationConstraint is never constructed with null.

String bucketRegion = bucketMetadata.bucketRegion();