Add a test for remote tool use by the agent (#30289)

- Adds a new smoke test for the use of the read_file tool by the agent
in an SSH project
- Fixes the SSH shutdown sequence to use a timer from the app's executor
instead of always using a real timer
- Changes the main executor loop for tests to advance the clock
automatically instead of panicking with `parked with nothing left to
run` when there is a delayed task

Release Notes:

- N/A

crates/gpui/src/executor.rs

@@ -281,6 +281,9 @@ impl BackgroundExecutor {
                         }
 
                         if !dispatcher.parking_allowed() {
+                            if dispatcher.advance_clock_to_next_delayed() {
+                                continue;
+                            }
                             let mut backtrace_message = String::new();
                             let mut waiting_message = String::new();
                             if let Some(backtrace) = dispatcher.waiting_backtrace() {