Clean up nanobind typing and source layout

tests/test_typing_artifacts.py

@@ -0,0 +1,18 @@
+from pathlib import Path
+
+import pytest
+
+ROOT = Path(__file__).resolve().parents[1]
+
+
+def test_checked_in_core_stub_exists():
+    assert (ROOT / "src" / "rpt" / "_core.pyi").exists()
+
+
+def test_checked_in_core_stub_matches_generated_stub():
+    generated_stub = ROOT / "build" / "bindings" / "rpt" / "_core.pyi"
+    if not generated_stub.exists():
+        pytest.skip("Build-generated nanobind stub is unavailable.")
+
+    checked_in_stub = ROOT / "src" / "rpt" / "_core.pyi"
+    assert checked_in_stub.read_text(encoding="utf-8") == generated_stub.read_text(encoding="utf-8")