minor #433 Add more instructions to CLAUDE.md file (OskarStark)

This PR was merged into the main branch.

Discussion
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 Add more instructions to `CLAUDE.md` file

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| Docs?         | no
| Issues        | --
| License       | MIT

Commits
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ad9626c Add more instructions to `CLAUDE.md` file

Author: OskarStark

CLAUDE.md

@@ -108,4 +108,7 @@ Each component uses:
 - Each component in `src/` is a separate Composer package with its own dependencies
 - Use `@dev` versions for internal component dependencies during development
 - Components follow Symfony coding standards and use `@Symfony` PHP CS Fixer rules
-- The monorepo structure allows independent versioning while maintaining shared development workflow
+- The monorepo structure allows independent versioning while maintaining shared development workflow
+- Do not use void return type for testcase methods
+- Always run PHP-CS-Fixer to ensure proper code style
+- Always add a newline at the end of the file