class_docstr: Determines the number of times a list crosses 0.
  Description:
      Given a list of numbers, return the number of times the value
      crosses 0. It is the number of times the value goes from a
      positive number to a negative number, or a negative number to
      a positive number. NaN values are ignored.
  Examples:
      >>> num_zero_crossings = NumZeroCrossings()
      >>> num_zero_crossings([1, -1, 2, -2, 3, -3])
      5
code: def get_function(self):
      def num_zero_crossings(x):
          cleaned = x[(x != 0) & (x == x)]
          signs = np.sign(cleaned)
          difference = np.diff(signs)
          crossings = np.where(difference)[0]
          return len(crossings)
  
      return num_zero_crossings
  
imports: import numpy
  from woodwork.column_schema import ColumnSchema
  from woodwork.logical_types import Integer
  from featuretools.primitives.base import AggregationPrimitive
label_desc: Use image node_id 1 for calling the NumZeroCrossings obj's underlying member method code with example usage: obj.get_function() and returns: num_zero_crossings, len