[FEATURE] Save map marker state and only rerender on new marker

[amandamartin-dev]

Description

Currently whenever a new event comes in to the app, the map component rerenders with all of the markers. This does not seem to create any issues and is a common implementation of leaflet in react, however, as an improvement to #66 it would be nice to only zoom to new map contributors instead of potentially zooming to the same person multiple times.

Edit: hold on this issue pending seeing how #66 does live. Perhaps no changes needed depending on UX with more data loading

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Additional information

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