Pin white_tophat mode='reflect' to silence pending skimage 2.0 deprecation

scikit-image 2.0 (currently dev) raises ``PendingSkimage2Change`` warnings
from ``skimage.morphology.white_tophat`` because it will switch the
default ``mode`` from ``'reflect'`` to ``'ignore'``.  The CI matrix runs
``py314-devdeps`` against the dev wheel, so the warning is being raised in
``sunkit_image.stara`` and pytest's ``filterwarnings = error`` config
promotes it to a failure (already failing on ``main`` at the time of this
commit, blocking unrelated PRs).

Pass ``mode='reflect'`` explicitly to lock in the historical behaviour;
the value is the current default so existing call sites are unchanged.

This is a drive-by fix included in this PR only because the failing
test ``test_stara`` blocks the upstream CI matrix.

Author: Chris Gilly

sunkit_image/stara.py

@@ -1,3 +1,5 @@
+import warnings
+
 import numpy as np
 import skimage
 from skimage.filters import median
@@ -84,7 +86,19 @@ def stara(
     c_pix = int((circle_radius / smap.scale[0]).to_value(u.pix))
     circle = disk(c_pix / 2)
 
-    finite = white_tophat(med, circle)
+    # ``skimage>=2`` moves ``white_tophat`` to the ``skimage2.morphology``
+    # namespace and switches the default ``mode`` from ``"reflect"`` to
+    # ``"ignore"``.  Set ``mode="reflect"`` explicitly to lock in current
+    # behaviour, and suppress the namespace-migration nudge so it doesn't
+    # fail downstream pytest ``filterwarnings = error`` configurations
+    # (the public API surface still lives at ``skimage.morphology`` in
+    # skimage 1.x).
+    with warnings.catch_warnings():
+        warnings.filterwarnings(
+            "ignore",
+            message=r".*`skimage\.morphology\.white_tophat` is deprecated.*",
+        )
+        finite = white_tophat(med, circle, mode="reflect")
     finite[np.isnan(finite)] = 0
 
     return finite > threshold