Remove support for legacy jUnit 4 Spock Groovy tests

[sabieber]

BREAKING CHANGE

• All unit tests written in Groovy with Spock need to be migrated to Kotlin or Java

Details

All tests have been migrated to jUnit 5 Kotlin or Java

Additional Notes

• This PR is related to PR: Remove support for legacy jUnit 4 Spock Groovy tests sirius-parent#69

Checklist

• Code change has been tested and works locally
• Code was formatted via IntelliJ and follows SonarLint & best practices
• Patch Tasks: Is local execution of Patch Tasks necessary? If so, please also mark the PR with the tag.

[Copilot]

Pull request overview

This PR removes remaining support code for legacy JUnit 4 / Spock (Groovy) tests and aligns the test setup documentation and IDE run configurations with the JUnit 5-based test infrastructure used in this repository.

Changes:

• Migrates the remaining JUnit 4-style assertThrows usage in Kotlin tests to JUnit 5’s Kotlin-friendly assertThrows.
• Removes Spock/JUnit 4 scenario-suite infrastructure and Groovy base specification classes from src/test.
• Updates testing documentation and replaces an IntelliJ Maven test run configuration with a JUnit run configuration excluding nightly tests.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/test/kotlin/sirius/kernel/nls/FormatterTest.kt	Switches assertThrows to JUnit 5 Kotlin API usage.
src/test/java/sirius/kernel/SiriusExtension.java	Cleans up Javadoc to match removed scenario-suite support.
src/test/java/sirius/kernel/ScenarioSuite.java	Removes legacy JUnit 4 / Spock-based scenario suite runner.
src/test/java/sirius/kernel/Scenarios.java	Removes legacy scenario annotation container.
src/test/java/sirius/kernel/Scenario.java	Removes legacy scenario annotation.
src/test/java/sirius/kernel/BaseSpecification.groovy	Removes Spock base specification class.
README.md	Documents SiriusExtension as the preferred way to run framework-backed tests.
.run/test.run.xml	Adds IntelliJ JUnit run configuration excluding nightly tests.
.run/mvn clean test - without nightly.run.xml	Removes IntelliJ Maven run configuration previously used to exclude nightly.

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