feat: graceful load failure for module-loading items

A self-loading item that can't load its module/file (unittest test file
with a missing import, pytest not installed on the host, ...) no longer
aborts the whole test load. TestSet._load_item() wraps load(), warns at
load time and records item._load_error; @test_run turns it into a clean
run-time FAILURE. The rest of the campaign loads and runs.

Scoped to module-loading items (unittest; pytest once merged). Structural
action loading stays fail-fast.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/testium/interpreter/test_items/test_item.py

@@ -61,6 +61,13 @@ def test_run(f):
 
         self.run_test_init()
 
+        # The item could not be loaded (e.g. a missing module): FAIL at run.
+        # run_test_end -> write_footer prints the message.
+        if self._load_error is not None:
+            self.result.set(TestValue.FAILURE, self._load_error)
+            self.run_test_end()
+            return self.result
+
         while self._is_paused:
             sleep(0.2)
             if self.isStopped() :
@@ -151,6 +158,7 @@ class TestItem:
         self._expected_result = None
         self._no_fail = None
         self._is_stopped = False
+        self._load_error = None
         self._is_running = False
         self._is_breakpoint = False
         self._is_paused = False

src/testium/interpreter/test_set.py

@@ -451,6 +451,20 @@ class TestSet:
     def rootItem(self):
         return self._rootItem
 
+    def _load_item(self, item):
+        """Run an item's self-load, deferring a failure (e.g. a missing module)
+        to a run-time FAILURE instead of aborting the whole test load."""
+        try:
+            return item.load()
+        except Exception as e:
+            msg = getattr(e, "_message", None) or str(e)
+            item._load_error = msg
+            tm.print_warn(
+                f"'{item.cmd()}' item '{item.name()}' could not be loaded: "
+                f"{msg} (it will FAIL at run)."
+            )
+            return {}
+
     def load_test_recursively(self, tree_parent, parent_seq, file_name):
         ret = {}
         try:
@@ -534,7 +548,7 @@ class TestSet:
                     # case where the test item loads itself its descendants
                     if it == cst_type.TYPE_UNITTEST:
                         item.setTestDir(test_dir)
-                        child = item.load()
+                        child = self._load_item(item)
                     elif issubclass(it.item_class, TestItemActions):
                         child = item.load()
                     # case where the test item is an items container