Improve memory usage

[neiljp]

For fairly "large" servers such as chat.zulip.org memory usage can be larger than one might expect, partially since we retain all the original data sent by the server and don't currently trim entries actively.

My current resident memory for two ZT sessions is at 160M & 398M; the latter has been running longer so may have accumulated more useful data, but both are quite large. The virtual memory used is much larger.

Due to ZT being isolated and easy to restart - useful during development too - this hasn't been a huge focus, but now seems like a promising time to investigate where our memory is going and particularly if there are some simple changes we can make initially.

My suspicions are that we may be regenerating UI elements more often than we need to, but measurements would help.

[neiljp]

See some initial analysis in the #zulip-terminal > Improve memory usage #T1028 topic on chat.zulip.org.