Loading emotes holds up other events

[lunar-seal]

Describe the bug

Loading emotes can hold up other events, such as sending a message.

Reproduction

1.Have about 1000 emotes
2. Open devtools, set speed to good 3g, disable cache
2. scroll through emotes
3. send a message
4. observe stalled message

Expected behavior

No response

Platform and versions

1. Linux
2. Firefox 153
3. Sable v1.20.1-nightly.260731094100-dev (a88774d)
4. Synapse 1.157.2

Additional context

No response

[lunar-seal]

Behavior improved by #1543

Keeping this issue open, as some more work can be done to improve this behavior.

One example - bad network conditions on the subway. In my testing, Sable still fetches media with lots of concurrent connections. This holds up text messages. Sable could detect this, and limit media loading.

A challenge with fixing this is that the user experience must not get worse on good connections
A bad connection and an overloaded homeserver must be distinguished.