Allow CELL and NBHD layers to be visible together

[jaspreetishar]

Motivation

• Users need to be able to view cell centroids (CELL layer) at the same time as neighborhood polygons (NBHD layer) without one toggling the other off.

Description

• Removed the behavior in js/ui/text_buttons.js that forced the NBHD layer off when the CELL button was turned on so CELL toggling no longer disables NBHD visibility.
• Updated the viz_nbhd_layer subscription in js/viz/landscape_ist.js to stop auto-disabling or re-enabling the CELL layer, CELL slider, and CELL button state when NBHD visibility changes, making NBHD visibility independent of CELL.
• Removed the now-unused new_toggle_cell_layer_visibility import from js/viz/landscape_ist.js as a cleanup after decoupling NBHD/CELL behavior.

Testing

• Ran npm run lint:js (ESLint) and it completed successfully.

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Codex Task