test: import qiskit eagerly in conftest to fix test_simulation isolation failures

tests/conftest.py

@@ -1 +1,17 @@
 """Pytest configuration for test suite."""
+
+# Import qiskit eagerly, once, at collection time — before any test enters a
+# ``patch.dict("sys.modules", ...)`` block. qiskit imports its standard-gate
+# library lazily; if that first import happens *inside* a patched sys.modules
+# context, patch.dict deletes the freshly-added qiskit submodule entries on
+# exit, leaving qiskit half-initialized. Subsequent qiskit use then raises
+# (e.g. ``TypeError: invalid input: Instruction(name='rcccx_dg', ...)``) when
+# tests are run in isolation. Loading qiskit here makes that first import a
+# clean no-op everywhere downstream. See issue #47.
+try:
+    import qiskit  # noqa: F401
+    from qiskit import qasm2, qasm3  # noqa: F401
+except ImportError:
+    # qiskit is an optional dependency; tests that need it will skip/fail on
+    # their own terms rather than being blocked by this safeguard.
+    pass