feat: highlight overlay for hover, multi-select, and custom colors

[BRaimbault]

Description

What

Replaces direct feature-state styling on the base source with a cloned "highlight overlay" — a small GeoJSON source + cloned GL layers drawn above each layer's own base layers — so hover and persistent selection can each highlight one or more features, in an optional custom color, without touching the base source.

Why

The previous model (setHoverState toggling feature-state.hover directly on the base source) only supported a single hovered feature per layer and had no concept of persistent multi-selection or per-highlight color. This change adds both.

Key changes

• Map#onMouseMove now tracks the hovered layer/feature and fires mouseenter/mouseleave events instead of writing hover state directly; Layer/LayerGroup gained an onMouseEnter/onMouseLeave option.
• Layer#highlight(ids, color) / Layer#select(ids, color) (and the same on LayerGroup) accept a single id or array of ids plus an optional color, and drive the new overlay (src/utils/highlightOverlay.js). Hover and selection share one highlight color by design — see the doc comment on highlight()/select().
• Layer#setVisibleIds/LayerGroup#setVisibleIds/Cluster#setVisibleIds filter which features render per layer, and drop any now-hidden id out of the highlight overlay too.
• Cluster's separate polygon source now refreshes correctly after setVisibleIds(), and its clusterLayer paint reacts to hover/selection like the other layer builders.
• Layer#setVisibility/removeFrom correctly show/hide and clean up the overlay's cloned layers along with the base ones.

Known issues

Highlighting a polygon-derived feature inside a Cluster subclass currently has no visible effect — documented in-code at src/layers/Cluster.js (the polygon-to-point conversion used for clustering). Root-caused but not fixed here; it's a bigger architectural change (a second overlay source scoped to the polygon source) better scoped as its own follow-up.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud