Pyflwdir

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* support py 3.11 and drop support for py 3.8

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New
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* add FlwdirRaster.ucat_volume & subgrid.ucat_volume methods

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New
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* `FlwdirRaster.smooth_rivlen` method to smooth river length with a moving window operation over a river network.

Changed
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* Move to flit and pyproject.toml for installation and publication
* drop support for python 3.7
* update docs to Sphinx pydata style

Bugfix
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* use np.uint64 as dtype for large arrays

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New
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* read_nextxy method to read binary nextxy data

Bugfix
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* Support -9 (river outlet at ocean) and -10 (inland river pit) pit values for nextxy data
* Fix 'argmin of an empty sequence' error in dem_dig_d4

Improved
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* improve gvf and manning estimates in river_depth method

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Improved
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* prioritize non-boundary cells with same elevation over boundary cells in dem.fill_depressions 17

Bugfix
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* fix dem_adjust method 16

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Improved
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* add new idxs_pit argument to dem.fill_depressions

Bugfix
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* min_rivdph argument was not always applied in FlwdirRaster.river_depth