Update widgets.py

Fixes an issue where when users are using folium map and explore outside of the bounds of the raster the tileserver is continuously queried resulting in excessive 404 errors.

localtileserver/widgets.py

@@ -14,8 +14,7 @@
 class LocalTileServerLayerMixin:
     """Mixin class for tile layers using localtileserver."""
 
-    # Prevent the client from being garbage collected
-    tile_server: TileClient
+    pass
 
 
 def get_leaflet_tile_layer(
@@ -176,6 +175,7 @@ def get_folium_tile_layer(
     # Safely import folium
     try:
         from folium import TileLayer
+        from traitlets import Tuple, Union
     except ImportError as e:  # pragma: no cover
         raise ImportError(f"Please install `folium`: {e}")
 
@@ -196,7 +196,7 @@ def get_folium_tile_layer(
         )
 
     class FoliumTileLayer(TileLayer, LocalTileServerLayerMixin):
-        pass
+        bounds = Union((Tuple(),), default_value=None, allow_none=True).tag(sync=True, o=True)
 
     source, created = get_or_create_tile_client(
         source,
@@ -213,7 +213,9 @@ class FoliumTileLayer(TileLayer, LocalTileServerLayerMixin):
     )
     if attr is None:
         attr = DEFAULT_ATTRIBUTION
-    tile_layer = FoliumTileLayer(tiles=url, attr=attr, **kwargs)
+    b = source.bounds()
+    bounds = ((b[0], b[2]), (b[1], b[3]))
+    tile_layer = FoliumTileLayer(tiles=url, bounds=bounds, attr=attr, **kwargs)
     if created:
         # HACK: Prevent the client from being garbage collected
         tile_layer.tile_server = source