[BUG] Disappearing NC Boundaries

[adamkendis]

Describe the bug
BoundaryLayer is losing map context on subsequent renders. When navigating back to the map after visiting a non-map page, NC boundaries don't render.

Probably a good opportunity to improve map performance:

• Instantiate shared mapbox instance outside of Map lifecycle methods.
• follow v1 implementation for map/visualizations pages. Map never unmounts - visualizations page is displayed over the Map page. This will make switching back to the Map page instant with no re-render.

To Reproduce
Steps to reproduce the behavior:

1. With client running locally, go to localhost:3000
2. Wait for request dots and boundaries to load.
3. Click any other link in header (any report, Contact Us, Blog)
4. Click Map
5. Request dots load but boundaries do not

Expected behavior
Boundaries display on subsequent renders.

Additional context