Iterative version of getFlattenedTree for improved performance on large datasets

[123joshuawu]

Addresses #84

Thank you for the great library, it has worked really well and achieved amazing results with our project.

Recently, we had a performance issue with a particularly large dataset. The tree contained roughly 140k nodes with the structure being 14 nodes containing around 10k direct children each.

This would take around 1-2 minutes to render.

Quick profiling showed that getFlattenedTree was taking around 1 minute to complete.

After changing the getFlattenedTree to an iterative implementation, the render time decreased drastically with profiling showing all getFlattenedTree calls completing within 100ms.

Would appreciate any comments or thoughts

[ViktorReib]

Any updates for this PR?

[Cireo]

I think maintainers aren't following PRs, last update to the repo was last September =(. Might have to fork or monkey-patch if you want it.

A little investigation on the last merged PR reveals that the owner became a father, so they probably reprioritized correctly!

[ojhawkins]

A long shot but any possibility of this being merged?