Leaflet styles are fetched every time component enters DOM

[it1shka]

Hi,

In the packages/graphic-walker/src/shadow-dom.tsx styles for Leaflet are included as a reference to CDN:

<link
    rel="stylesheet"
    href="https://unpkg.com/leaflet@1.9.4/dist/leaflet.css"
    integrity="sha256-p4NxAoJBhIIN+hmNHrzRCf9tD/miZyoHS5obTRR9BMY="
    crossOrigin=""
/>

I got a customer complaint that in their case every time when they opened graphic-walker widget,
the style for leaflet was re-fetched from CDN. That was applying pressure to the network bandwidth

[it1shka]

I believe this may resolve the problem:
#500