Retest extension integrations

[avandenberghe]

Description

The following extension integrations need to be retested with 3.0.4 to confirm they still work:

• phpbb/topicprefixes (official Topic Prefixes) — not wired in services.yml, may not actually be supported
• part3/topicprefixes (Stathis) — injected via @?part3.topicprefixes.functions
• imkingdavid/prefixed (Pre:fixed) — injected via @?prefixed.manager, used as fallback
• phpbb/collapsiblecategories — injected via @?phpbb.collapsiblecategories.operator
• mChat — template event recenttopics_mchat_side in side view

Notes

• Some of these extensions may be abandoned or incompatible with phpBB 3.3 / PHP 8.x
• If an integration no longer works or the extension is unmaintained, consider removing the optional service injection and updating the README