Add slow-test reporting to nextest in CI (#15662)

This is helpful for spotting tests that are running slow. In uv, we use
a 10s threshold. Here, it looks like we could use something smaller.

e.g.

<img width="964" alt="Screenshot 2025-01-21 at 6 08 00 PM"
src="https://github.com/user-attachments/assets/b32bbc61-9815-4a43-938d-17cd0cf8b0de"
/>

.config/nextest.toml

@@ -6,3 +6,10 @@ failure-output = "immediate-final"
 fail-fast = false
 
 status-level = "skip"
+
+# Mark tests that take longer than 1s as slow.
+# Terminate after 60s as a stop-gap measure to terminate on deadlock.
+slow-timeout =  { period = "1s", terminate-after = 60 }
+
+# Show slow jobs in the final summary
+final-status-level = "slow"