an infinite-canvas terminal multiplexer using gpui

tarp: spawn terminals over the attached connection #4

Open eti.tf
targeting op/kmwmtpnqoxwu from eti.tf/tarp:eti/attached-spawn
Open opened by and assigned to eti.tf
targeting op/kmwmtpnqoxwu from eti.tf/tarp:eti/attached-spawn

terminals now spawn through the host's existing connection instead of opening a new connection for each spawn. adds Handle::call_blocking, whose response is delivered by the read thread so it is answered while the UI thread is blocked, and removes the stored EndpointAddr. based on op/kmwmtpnqoxwu.

Commits 1

tarp: spawn terminals over the attached connection