Use JavaBestPractices in RecipeTestingBestPractices

[timtebeek]

Summary

• Replace individual UseVarForConstructors, UseVarForPrimitive, and UseVarForTypeCast recipes in RecipeTestingBestPractices with the composite org.openrewrite.java.migrate.JavaBestPractices recipe
• Scoped to test recipes only since JavaBestPractices includes an upgrade to Java 25

Test plan

• Verify the YAML parses correctly and recipes resolve
• Run mvn test to confirm no regressions

[timtebeek]

Depends on

• Use Java 25 toolchain going forward rewrite-build-gradle-plugin#154
• Run CI on Java 25 by default gh-automation#86