added template for making views (#377)

Cleaned up the helper functions by: 
- Added template for make_view (and new make_const_view) instead of the
copy paste implementation
- checks c_style and dimensions inside make_view
- test binding to be able to probe the checks in make_view

Call sites can be reviewed in a second PR since usage of const or
strictness of conversion depends...

python/tests/test_make_view.py

@@ -0,0 +1,74 @@
+# SPDX-License-Identifier: MPL-2.0
+"""Probe make_view in np_helper.hpp through the bindings in _aare.testing"""
+import numpy as np
+import pytest
+
+from aare._aare import testing
+
+
+
+
+def test_make_view_roundtrip():
+    """Send an array to C++ and check that we get the same array back"""
+    arr = np.arange(30, dtype=np.float64).reshape(5, 6)
+    out = testing.view_roundtrip_2d(arr)
+    np.testing.assert_array_equal(out, arr)
+
+    #Sanity check to make sure we got a copy an not just the same thing back
+    arr[3,2] = 31655
+    assert arr[3,2] != out[3,2]
+
+def test_make_view_const_roundtrip():
+    """Const works if the array is not writeable"""
+    arr = np.arange(30, dtype=np.float64).reshape(5, 6)
+    arr.flags.writeable = False
+    out = testing.const_view_roundtrip_2d(arr)
+    np.testing.assert_array_equal(out, arr)
+
+def test_make_view_const_roundtrip_writable():
+    """Const works also if the array is  writeable"""
+    arr = np.arange(30, dtype=np.float64).reshape(5, 6)
+    out = testing.const_view_roundtrip_2d(arr)
+    np.testing.assert_array_equal(out, arr)
+
+def test_make_view_fill():
+    arr = np.arange(30, dtype=np.float64).reshape(5, 6)
+    testing.view_fill_2d(arr, 7)
+    assert (arr == 7).all()
+
+def test_make_view_fill_rejects_nonwriteable():
+    arr = np.arange(30, dtype=np.float64).reshape(5, 6)
+    arr.flags.writeable = False
+    with pytest.raises(ValueError, match="not writeable"):
+        testing.view_fill_2d(arr, 7)
+
+def test_make_view_2d_rejects_1d():
+    arr = np.arange(30, dtype=np.uint16)
+    with pytest.raises(ValueError, match="Expected 2D array, got 1D"):
+        testing.view_roundtrip_2d(arr)
+
+def test_make_view_2d_rejects_3d():
+    arr = np.arange(30, dtype=np.uint16).reshape(3, 5, 2)
+    with pytest.raises(ValueError, match="Expected 2D array, got 3D"):
+        testing.view_roundtrip_2d(arr)
+
+def test_make_view_rejects_noncontiguous():
+    arr = np.arange(30, dtype=np.float64).reshape(5, 6)
+    arr = arr[::2, ::3]  # non-contiguous
+    assert not arr.flags.c_contiguous
+    with pytest.raises(ValueError, match="not C-contiguous"):
+        testing.view_roundtrip_2d(arr)
+
+def test_make_view_rejects_noncontiguous_const():
+    arr = np.arange(30, dtype=np.float64).reshape(5, 6)
+    arr = arr[::2, ::3]  # non-contiguous
+    assert not arr.flags.c_contiguous
+    with pytest.raises(ValueError, match="not C-contiguous"):
+        testing.const_view_roundtrip_2d(arr)
+
+def test_make_view_rejects_fortran_order():
+    arr = np.asfortranarray(np.arange(30, dtype=np.float64).reshape(5, 6))
+    assert not arr.flags.c_contiguous
+    with pytest.raises(ValueError, match="not C-contiguous"):
+        testing.view_roundtrip_2d(arr)
+