Support more graphs for phate.fit

[dsm-72]

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See this:

PHATE/Python/phate/phate.py

Line 688 in 8578022

if isinstance(X, graphtools.graphs.LandmarkGraph) or (

The result is that if gt.Graph(...) yields something like kNNGraph it will get converted to another graph object e.g. TraditionalGraph.

Describe the solution you'd like
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Let me pass in a graph for fit / fit_transform and have that graph be stored under phate.graph

Describe alternatives you've considered
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keeping both objects around.

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