feat(column): add exclude_from_color_key field to ColumnChart

[palewire]

refactor(value_labels): remove value_labels_always from serialization

[Copilot]

Pull Request Overview

This PR removes the redundant value_labels_always field from the ValueLabels deserializer output and adds support for excluding columns from the color key in column charts.

• Removes value_labels_always from deserialization output as it's redundant (the show_value_labels field already captures this information)
• Adds exclude_from_color_key field to ColumnChart with proper serialization support
• Updates all related test assertions to reflect the removed field

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
datawrapper/charts/serializers/value_labels.py	Removes redundant value_labels_always field from deserialize method output
tests/unit/serializers/test_value_labels.py	Updates test assertions to remove checks for value_labels_always field
datawrapper/charts/column.py	Adds exclude_from_color_key field and integrates it into color category serialization

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