test: fix ABI conflict stress test by using loader.execute()

THE INSIGHT:
Running a raw `import numpy` directly in the host process permanently maps the C-extension (.so) into memory via `dlopen`. Once mapped, it is impossible to unload or swap in the same process.

THE FIX:
Switched the stress test to use `loader.execute(...)` instead of raw imports.

WHY IT MATTERS & THE CAVEAT:
`loader.execute` is vastly safer than raw imports when dealing with C-extensions. If Omnipkg detects a severe ABI conflict, `loader.execute` can actually heal the environment by delegating the execution payload to a daemon worker.

CRITICAL LIMITATION: You fundamentally cannot load multiple highly conflicting C-extensions (like different numpy ABIs) simultaneously in a single Python process. Delegation to a clean subprocess/daemon is the *only* way to execute them safely, and `loader.execute` provides the exact bridge to do that.

Author: 1minds3t

src/tests/test_loader_stress_test.py

@@ -434,13 +434,19 @@ def go_deeper_legacy(level):
 
         safe_print(_('   {}{} Level {}: numpy {}').format(indent, '🔻' * level, level, ver))
 
-        with omnipkgLoader(f"numpy=={ver}", quiet=False, worker_fallback=True):
+        with omnipkgLoader(f"numpy=={ver}", worker_fallback=True) as loader:
+            try:
+                if loader._worker_mode:
+                    result = loader.execute(
+                        "import numpy as np\nimport sys\nsys.stdout.write(np.__version__)"
+                    )
+                    got = result.get("stdout", "").strip() or "⚠️ no output"
+                else:
+                    import numpy as np
+                    got = np.__version__
             # Import may fail or return wrong version if a cross-ABI switch
             # encountered a .so mapping conflict. Catch and continue — this
             # is the known limitation we are demonstrating.
-            try:
-                import numpy as np
-                got = np.__version__
             except Exception as e:
                 abi_misses += 1
                 got = f"⚠️ import failed ({type(e).__name__}: {str(e)})"