Stats worker may return a complex when pygeoprocessing is built with Cython >= 3.0.0

[phargogh]

I came across this exception after rebuilding my container for NCI (forgive the line numbers):

8163 Traceback (most recent call last):
8164   File "/opt/conda/lib/python3.9/multiprocessing/pool.py", line 125, in worker
8165     result = (True, func(*args, **kwds))
8166   File "/home/users/jadoug06/workspace/2021-nci-ndr-sherlock/prep-ndr-inputs-pipeline.py", line 245, in intensified_rainfed_n_app
8167     pygeoprocessing.raster_calculator(
8168   File "/opt/conda/lib/python3.9/site-packages/pygeoprocessing/geoprocessing.py", line 569, in raster_calculator
8169     float(target_stddev))
8170 TypeError: can't convert complex to float

It turns out that in Cython 3.0.0, they included the following change:

The ** power operator now behaves more like in Python by returning the correct complex result if required by math. A new cpow directive was added to turn on the previous C-like behaviour. (Github issue #4936)

When the raster_calculator stats worker does its final computation for the standard deviation, it does the following, taking the square root by way of raising to the 0.5 power:

    if n > 0:
        stats_work_queue.put(
            (min_value, max_value, M_local,
                (S_local / <double>n) ** 0.5))