Replace deprecated remove_small_objects(min_size=...) in cloud-mask preprocessing without changing threshold behavior

[Copilot]

SDS_preprocess.create_cloud_mask was emitting repeated FutureWarnings under scikit-image 0.26+ because it still used the deprecated min_size parameter. This PR migrates those calls to max_size while preserving existing object-removal thresholds exactly.

• Deprecation migration in SDS_preprocess.create_cloud_mask

  • Updated cloud mask cleanup call from min_size=40 to max_size=39.
  • Updated cloud_mask_issue cleanup call from min_size=100 to max_size=99.
  • Uses the required off-by-one mapping to keep prior semantics (remove < T ↔ remove <= T-1).

• Behavior-preservation regression coverage

  • Added focused tests for connected-component thresholds in:
    • tests/test_create_cloud_mask_thresholds.py
  • Verifies boundary behavior is unchanged:
    • 39 removed / 40 kept
    • 99 removed / 100 kept
  • Also asserts the primary path no longer emits the deprecation warning from remove_small_objects.

# Before
morphology.remove_small_objects(cloud_mask, min_size=40, connectivity=1)

# After (equivalent behavior on threshold boundary)
morphology.remove_small_objects(cloud_mask, max_size=39, connectivity=1)

Original prompt

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This section details on the original issue you should resolve

<issue_title>Deprecation warning in SDS_preprocess.py due to remove_small_objects(min_size=...)</issue_title>
<issue_description>## Description

Running CoastSeg triggers repeated FutureWarning messages from coastsat/SDS_preprocess.py related to a deprecated parameter in skimage.morphology.remove_small_objects.

The warning points to:

File: coastsat/SDS_preprocess.py

Line: 973

Warning

C:\development\doodleverse\coastseg\CoastSeg\.pixi\envs\default\Lib\site-packages\coastsat\SDS_preprocess.py:973: FutureWarning: Parameter `min_size` is deprecated since version 0.26.0 and will be removed in 2.0.0 (or later). To avoid this warning, please use the parameter `max_size` instead. For more details, see the documentation of `remove_small_objects`. Note that the new threshold removes objects smaller than **or equal to** its value, while the previous parameter only removed smaller ones.
  cloud_mask = morphology.remove_small_objects(

This warning is emitted multiple times during execution.

Cause

skimage.morphology.remove_small_objects() has deprecated the min_size parameter as of scikit-image 0.26.0. The code in SDS_preprocess.py still appears to use min_size, which will eventually break once support is removed in scikit-image 2.0.0 or later.

Suggested fix

Update the call at SDS_preprocess.py:973 to use max_size instead of min_size, while preserving current behavior as closely as possible.

One thing to note from the warning:

max_size removes objects smaller than or equal to the threshold

min_size previously removed objects only smaller than the threshold

So the replacement may need an off-by-one adjustment depending on intended behavior.</issue_description>

<agent_instructions>Create a fix for this issue. Ensure the same behavior is maintained while fixing the deprecation warning.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes Deprecation warning in SDS_preprocess.py due to remove_small_objects(min_size=...) #22

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