Use cv.dilate for dilation

[cpaniaguam]

In [23]: import cv2
    ...: from skimage import io
    ...: from skimage.morphology import disk
    ...: import numpy as np
    ...:
    ...: landmask = io.imread("./test/test_inputs/landmask.tiff")[:, :, 0]
    ...: selem = disk(50).astype(np.uint8)
    ...:

In [24]: %%timeit
    ...: cv2.dilate(landmask, selem)
    ...:
    ...:
2.92 s ± 11.7 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)

[cpaniaguam]

After adding this feature, update this test to compare the disk(50) se generator make_landmask_se against the one on file.

https://github.com/WilhelmusLab/IceFloeTracker.jl/blob/f3e5388f77cd99c5d4c0aae2776e7dbf1da07935/test/test-create-landmask.jl#L19