Move some logic from the template to .module

Problem/Motivation

The template of the block contains some logic that can be moved to .module file

 {% set safe_hash = configuration['block_revision_id'] ~ '--' ~ loop.index %}
                {# Setup our image style. #}
                {% set media_image = ''%}
                {% set image_desktop = ''%}
                {% if item.field_media.entity.field_media_image.entity.uri.value %}
                  {% set media_image = item.field_media.entity.field_media_image.entity.uri.value %}
                  {% set image_alt = item.field_media.entity.field_media_image.0.alt %}
                {% endif %}

                {% if media_image %}

Proposed resolution

Move that logic to the .module file directly.