fix: remove old map layers before rendering new layers

[wang-boyu]

Fix #192

Layers were added to leaflet map at each model step, but were never removed. This resulted in too many layers to be unnecessarily rendered when model kept running (shown below).

This fix removes old layers before new layers are added into leaflet map.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.21%. Comparing base (b717971) to head (c307dbc).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #194      +/-   ##
==========================================
+ Coverage   78.17%   78.21%   +0.03%     
==========================================
  Files          10       10              
  Lines         692      693       +1     
  Branches      151      151              
==========================================
+ Hits          541      542       +1     
  Misses        127      127              
  Partials       24       24              

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[wang-boyu]

Hi @rht @Corvince @EwoutH not sure whether this is a good time to ask, but would you like to take a look at this PR? Thanks!

[EwoutH]

I’m not too familiar with this part of the code base, but I see nothing weird.

[wang-boyu]

Thanks @EwoutH !