Removing deprecated use of lmfit (#344)

Removed the lmfit based fitting and the old API for calling functions

closes #296

python/tests/test_Fit.py

@@ -0,0 +1,15 @@
+# SPDX-License-Identifier: MPL-2.0
+import numpy as np
+import aare
+
+
+
+def test_gaussian_model_evaluates_and_fits_data():
+    x = np.linspace(-5.0, 5.0, 51)
+    expected = np.array([20.0, 0.5, 1.2])
+    model = aare.Gaussian()
+
+    y = model(x, expected)
+    result = model.fit(x, y)
+
+    np.testing.assert_allclose(result["par"], expected, atol=2e-3)