Refactor StitchAction and its tests to Kotlin (CATROID-1584, CATROID-1585)

[harshsomankar123-tech]

Related Issues

• Resolves CATROID-1584: REFACTOR StitchAction to Kotlin (https://catrobat.atlassian.net/browse/CATROID-1584)
• Resolves CATROID-1585: REFACTOR tests of StitchAction to Kotlin(https://catrobat.atlassian.net/browse/CATROID-1585)

Description
This PR refactors the StitchAction class and its corresponding instrumented test StitchActionTest from Java to idiomatic Kotlin.

Key Changes

StitchAction.kt:

• Converted core logic to idiomatic Kotlin.
• Implemented Null Safety using safe calls (?.) and the Elvis operator (?:) to prevent NullPointerExceptions, fulfilling the requirement to eliminate !! assertions in production code.
• Updated property access for zIndex and embroideryThreadColor.

StitchActionTest.kt:

• Refactored the test suite to Kotlin.
• Optimized the mock setup to use lateinit var for the embroideryPatternManagerMock, allowing for cleaner verify calls without null-check clutter or !!.
• Corrected type handling for zIndex which is now safely handled as an Int.

General:

• Updated copyright headers to 2026.
• Verified that the project compiles and builds successfully.

Type of Change

• Refactoring (non-breaking change which improves code structure/readability)

How Has This Been Tested?

• Build Verification: Successfully ran ./gradlew assembleCatroidDebugAndroidTest to ensure all Kotlin components and test dependencies are correctly configured.
• Static Analysis: Verified that no !! assertions are used in the core logic and that null-safety patterns are correctly applied.

Your checklist for this pull request

Please review the contributing guidelines and wiki pages of this repository.

• Include the name of the Jira ticket in the PR’s title
• Include a summary of the changes plus the relevant context
• Choose the proper base branch (develop)
• Confirm that the changes follow the project’s coding guidelines
• Verify that the changes generate no compiler or linter warnings
• Perform a self-review of the changes
• Verify to commit no other files than the intentionally changed ones
• Include reasonable and readable tests verifying the added or changed behavior
• Confirm that new and existing unit tests pass locally
• Check that the commits’ message style matches the project’s guideline
• Stick to the project’s gitflow workflow
• Verify that your changes do not have any conflicts with the base branch
• After the PR, verify that all CI checks have passed
• Post a message in the catroid-stage or catroid-ide Slack channel and ask for a code reviewer

[github-advanced-security]

detekt found more than 20 potential problems in the proposed changes. Check the Files changed tab for more details.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[harshsomankar123-tech]

@reichli @dorianpercic PTAL