Sticky column native

[Castellon-ACM]

Summary

Extends the Sticky Column feature to the native core/columns block, previously only available for generateblocks/grid.

Changes

• JSX editor panel (frontblocks-sticky-column-option.jsx): Added core/columns to SUPPORTED_BLOCKS array; block name checks updated throughout to use the array.
• JS frontend (frontblocks-sticky-column.js): Rewrote the sticky implementation from scroll-event-based class toggling to applying position: sticky directly via inline styles. Uses :scope > .gb-grid-column, :scope > .wp-block-column selector to target child columns. For native wp-block-columns, creates a .frontblocks-sticky-inner wrapper div around all children and sets wrapper.style.alignItems = 'flex-start' to prevent stretch alignment from breaking sticky behaviour.
• CSS (frontblocks-sticky-column.css): Removed class-based sticky rules. Simplified to a single mobile override using position: relative !important for both .gb-grid-column .gb-container and .wp-block-column.
• PHP render (StickyColumn.php): Added add_sticky_attributes_to_columns_block() delegating to the shared add_sticky_attributes() helper; added register_sticky_attributes_for_columns_block() via register_block_type_args to register frblStickyEnabled, frblStickyOffset, and frblStickyColumnIndex on core/columns.

[davidperezgar]

Fix the conflict before merge