ci: run the action-matrix sample on its own; name a hang in an edit round (#1037)

The sampled pi-case hole on Body1/F13:side:[email protected] became a real hole with #952 (7.5 s instead of 170 ms); beside the heavy tests on main's push runs it passed the matrix's 90 s action limit in its edit round, reported as the design not loading. The sample now takes every CPU in nextest so nothing runs beside it, and the edit round writes a start line so a hang there is reported as <action>+edit.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

.config/nextest.toml

@@ -28,3 +28,11 @@ slow-timeout = { period = "60s" }
 
 [profile.ci.junit]
 path = "junit.xml"
+
+# The action matrix sample runs its designs in parallel worker processes, one per CPU. Run with
+# other tests beside it (the heavy ones on main), a pi-case hole that takes 8 s alone (#952 makes
+# it a real hole) went past the matrix's 90 s action limit. It runs on its own.
+[[profile.ci.overrides]]
+filter = "binary(action_matrix) & test(=action_matrix_sample)"
+threads-required = "num-cpus"
+