rm-hull / maps / 25607532072

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feat: Add Contour Lines overlay and MapLibreLayer component (#1188)

* wip

* working but crap

* feat: improve MapLibreLayer opacity handling

Refactored `MapLibreLayer` to handle opacity transitions more accurately
by snapshotting original layer opacities and applying them as a
multiplier. This ensures that layers with different base opacities
retain their relative transparency levels.

- Added support for `background`, `circle`, `fill-extrusion`, `haze`,
  `raster`, and `symbol` layer types.
- Snapshots are captured on initial load and re-captured when the
  underlying style URL changes.
- Updated **Contour Lines** overlay configuration to improve visibility
  at lower zoom levels and corrected the display name.

```mermaid
sequenceDiagram
    participant App as React Component
    participant ML as MapLibreLayer
    participant Map as MapLibre Map
    App->>ML: New opacity prop
    alt Snapshot not initialized
        ML->>Map: getStyle()
        Map-->>ML: Style Specification
        ML->>ML: buildOpacitySnapshot()
    end
    ML->>ML: applyOpacity(opacity * base)
    ML->>Map: setPaintProperty() for all layers
```

* fix: support expressions and fix opacity handling

This change improves how layer opacity is managed by supporting MapLibre
expressions and preventing progressive value degradation.

- Use a `WeakMap` to store opacity snapshots securely against layer
  instances.
- Support MapLibre expressions (e.g., zoom-based interpolation) by using
  the `["*", value, opacity]` expression for scaling.
- Fix a typo in `OPACITY_PROPERTIES` where `haze` was used instead of
  `heatmap`.
- Ensure snapshots are cleared and rebuilt when the map style changes to
  avoid applying values to non-existent or different layers.
- Add comprehensive unit tests for internal opacity logic.

```mermaid
sequenceDiagram
    participant C as MapLibreLayer
    participant W as WeakMap (Snapshots)
    participant M as MapLibre Map

    C->>M: withStyleLoaded()
    M-->>... (continued)

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