refactor(matrix-client): optimize room tags fetching by using in-memory data instead of network requests

[domw30]

What does this do?

• We're eliminating network requests for room tags by accessing the data directly from Room objects already in memory.

Why are we making this change?

• To significantly improve initial load performance by removing unnecessary network requests and making room tags immediately available during conversation loading.

How do I test this?

• run tests as usual.
• run the UI, monitor initial load of the app

Key decisions and Risk Assessment:

Things to consider:

1. How will this affect security?
2. How will this affect performance?
3. Does this change any APIs?