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This is a rather large PR. The highlights are as follows:

1. Two bug fixes: The first one is related to the wrong assignment of lon from the xsatendpoints endpoint input in this line of code. The second one was wrong upper limit for an iterator of one of the for-loops in tspline function in this line of code.
2. Significant performance improvement in computing tension spline by using numba. The __calc_curvature was refactored to take advantage of numba's parallel range since this function is embarrassingly parallel.
3. Using pygeoogc and async_retriever for querying the 3DEP index RESTful service. These two libraries offer more stability and robustness for working with web services.
4. Some improvements in computing distances between points in a geopandas.geoDataFrame.
5. Change type hinting of array-like objects from numpy.typing.NDArray to numpy.ndarray since the new numpy.typing module has been recently introduced to numpy v1.21 and numba still does not support this version of numpy.
6. Some other minor improvemnts.