fix return-value/deprecated API bugs, accumulation lock leaks, code cleanup

- raise instead of silent None for unsupported operands and empty negation
- validate before acquiring lock in Accumulation operators (no RLock leak)
- Accumulation._copy_provenance helper, ADC_Result._copy_metadata for all result paths
- shared _sandbox_stdout_redirect contextmanager for sandboxed scripts
- TemperatureMonitor dead code removal (gtk helper, traceback, unused properties)
- new unit tests incl. lock-freedom regression test
- gitignore sphinx generated doc/_autosummary/ and doc/damaris/

tests/test_DamarisFFT.py

@@ -0,0 +1,44 @@
+import unittest
+
+import numpy as np
+
+from damaris.data.DamarisFFT import DamarisFFT
+
+
+class TestDamarisFFT(unittest.TestCase):
+    @staticmethod
+    def make_fft():
+        fft = DamarisFFT()
+        fft.sampling_rate = 100.0
+        fft.x = np.arange(10, dtype="float32") / 100.0
+        fft.y = [np.arange(10, dtype="float32")]
+        fft.xlabel = "Time / s"
+        return fft
+
+    def test_clip_without_arguments_is_placeholder(self):
+        """clip() without arguments returns self unchanged (placeholder use)."""
+        fft = self.make_fft()
+        self.assertIs(fft.clip(), fft)
+        self.assertEqual(len(fft.x), 10)
+        np.testing.assert_array_equal(fft.y[0], np.arange(10, dtype="float32"))
+
+    def test_clip_swaps_reversed_bounds(self):
+        fft = self.make_fft()
+        fft.clip(start=0.05, stop=0.01)
+        expected_x = (np.arange(10, dtype="float32") / 100.0)[1:5]
+        np.testing.assert_array_equal(fft.x, expected_x)
+        np.testing.assert_array_equal(fft.y[0], np.arange(1, 5, dtype="float32"))
+
+    def test_clip_single_bound(self):
+        fft = self.make_fft()
+        fft.clip(start=0.02)
+        self.assertEqual(len(fft.x), 7)
+        self.assertEqual(len(fft.y[0]), 7)
+
+    def test_clip_too_close_raises(self):
+        fft = self.make_fft()
+        self.assertRaises(ValueError, fft.clip, 0.021, 0.029)
+
+
+if __name__ == "__main__":
+    unittest.main()