Bug caused by joining the "!****:matrix.org" room with over 100,000 people

*This issue was originally created by [**@simontxxx**](https://github.com/simontxxx) at .*

### Background information

- **Dendrite version or git SHA**: 46902e5766cc8efcc4f1abb38789f8179893c17d
- **SQLite3 or Postgres?**: Posgtres
- **Running in Docker?**: no
- **`go version`**: 1.22.2
- **Client used (if applicable)**: Element

### Description

- **What** is the problem: CPU usage is high. Missing event has missing prev events". Many log "Failed to get missing /event for event ID". There is a problem with message consumption in Nats, and messages are starting to get stuck. This is causing the recipient to not receive messages when they are sent. Removed the jetstream directory of nats and restart dendrite to recover.
- **Who** is affected: "Me" - Who are you? Running the server or a user on a Dendrite server?
- **How** is this bug manifesting: “Can't send messages"
- **When** did this first appear:

### Steps to reproduce

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