Fix Hwloc CPU core detection returning 0 in CI environments

Apply the same fix from ModelingToolkit.jl (d7f7ed0) to handle cases where
Hwloc.num_physical_cores() and Hwloc.num_virtual_cores() return 0 in certain
CI environments.

This prevents the "input string is empty" parse error by ensuring we always
have at least 1 core.

🤖 Generated with [Claude Code](https://claude.ai/code)

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

Author: claude

test/runtests.jl

@@ -23,14 +23,14 @@ const RETESTITEMS_NWORKERS = if GROUP == "wrappers"
 else
     parse(
         Int, get(ENV, "RETESTITEMS_NWORKERS",
-            string(min(ifelse(Sys.iswindows(), 0, Hwloc.num_physical_cores()), 4))
+            string(min(ifelse(Sys.iswindows(), 0, max(Hwloc.num_physical_cores(), 1)), 4))
         )
     )
 end
 const RETESTITEMS_NWORKER_THREADS = parse(Int,
     get(
         ENV, "RETESTITEMS_NWORKER_THREADS",
-        string(max(Hwloc.num_virtual_cores() ÷ max(RETESTITEMS_NWORKERS, 1), 1))
+        string(max(max(Hwloc.num_virtual_cores(), 1) ÷ max(RETESTITEMS_NWORKERS, 1), 1))
     )
 )