Fix Image.clip_to_dtype and Image.astype with Dask arrays

[kostrykin]

No description provided.

[Copilot]

Pull request overview

This PR fixes compatibility issues with Dask arrays in the Image.clip_to_dtype and Image.astype methods by introducing helper functions that handle both NumPy and Dask array types appropriately.

• Introduces _get_min_max_values() helper function to efficiently compute min/max values for both NumPy and Dask arrays
• Introduces _unique() helper function to compute unique values for both NumPy and Dask arrays
• Adds comprehensive test coverage for Dask arrays by creating new test classes that inherit from mixin classes

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
giatools/image.py	Adds _get_min_max_values() and _unique() helper functions; updates astype() and clip_to_dtype() methods to use these helpers instead of calling array methods directly
tests/unit/test__image.py	Adds mocks for new helper functions to ensure unit tests remain isolated
tests/module/test__image.py	Refactors test structure with mixins to enable testing both NumPy and Dask arrays; adds ImageTestCase__dtype_mixin__dask class and separate test classes for Dask array testing

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[github-actions]

Test coverage results for ac17eb1:

• 🧩 Unit tests: 74%
• 📦 Module tests: 55%
• 🔄 Integration tests: 87%
• Total coverage: 98%