[FSTORE-1912] java client-fix for 400 error code change for feature group not found

[dhananjay-mk]

This PR adds/fixes/changes...

• please summarize your changes to the code
• and make sure to include all changes to user-facing APIs

JIRA Issue: -

Priority for Review: -

Related PRs: -

How Has This Been Tested?

• Unit Tests
• Integration Tests
• Manual Tests on VM

Checklist For The Assigned Reviewer:

- [ ] Checked if merge conflicts with master exist
- [ ] Checked if stylechecks for Java and Python pass
- [ ] Checked if all docstrings were added and/or updated appropriately
- [ ] Ran spellcheck on docstring
- [ ] Checked if guides & concepts need to be updated
- [ ] Checked if naming conventions for parameters and variables were followed
- [ ] Checked if private methods are properly declared and used
- [ ] Checked if hard-to-understand areas of code are commented
- [ ] Checked if tests are effective
- [ ] Built and deployed changes on dev VM and tested manually
- [x] (Checked if all type annotations were added and/or updated appropriately)

[Copilot]

Pull request overview

The Hopsworks backend changed the HTTP status code returned when a feature group is not found from 404 to 400, while keeping the same errorCode (270009). The Java client's getOrCreateFeatureGroup was matching on both the Error: 404 substring and the error code, so after the backend change it would propagate the error instead of creating the feature group. This PR loosens the match to rely on the error code only, and adds unit tests covering both the not-found-and-create path and the rethrow path.

Changes:

• Drop the Error: 404 substring check in FeatureGroupEngine.getOrCreateFeatureGroup, keeping only the errorCode:270009 check so both 400 and 404 responses trigger creation.
• Add TestFeatureGroupEngine with tests for the 400-not-found path, the existing-FG path, and rethrow of unrelated errors.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
java/hsfs/src/main/java/com/logicalclocks/hsfs/engine/FeatureGroupEngine.java	Relax the error matcher so the not-found-and-create branch triggers regardless of HTTP status code.
java/hsfs/src/test/java/com/logicalclocks/hsfs/engine/TestFeatureGroupEngine.java	New unit tests for getOrCreateFeatureGroup covering create-on-not-found, existing FG, and rethrow paths.

[github-actions]

Coverage report

This PR does not seem to contain any modification to coverable code.