fix: DataFilterExtension get_filter_category

[ATL2001]

as we discussed in discussion #711 I was unable to get the DataFilterExtension to work for filtering data with categories.

I finally spent some time looking into what was going on, and the FilterValueAccessor was being used for the get_filter_category property, but that accessor is set up to work in conjunction with the filter_size parameter of the DataFilterExtension. I created a new FilterCategoryAccessor accessor modeled after the FilterValueAccessor that works with the category_size parameter and does not do any casting of values to Float32, because looking at the DeckGL docs it appears that the category_filter should be able to work with string data.

Using the new accessor for the get_filter_category on the data filter extension I'm now able to change filter_categories on the layer and the features are filtered as expected for numeric data. What I've got still isn't working for filtering with string data, but I figured this was worth throwing out there to see if anyone else had an idea how to get the filter working with those as well.

I've added a notebook to the examples folder that I do not intend to actually check into the repo, which creates a DFE for a layer and links it to a widget to show that the category_filter is working for the numeric data, but not the string data. If we get the strings working I'd be happy to make a better example notebook that showcases category filters

[ATL2001]

a couple screenshots to show the selector changing the filtered points on my map: