Replace use of deprecated is_NumberFieldElement

cutgeneratingfunctionology/igp/crazy_perturbation.sage

@@ -248,7 +248,7 @@ def is_in_ZZ_span(x, generators):
     numbers = [x]+generators
     if not is_all_the_same_number_field_fastpath(numbers):
         numbers = nice_field_values(numbers, RealNumberField)
-        if not is_NumberFieldElement(numbers[0]):
+        if not isinstance(numbers[0], NumberFieldElement_base):
             if is_all_QQ(numbers):
                 raise ValueError("generators are not Q-linear independent")
             raise ValueError("Q-linear independence test only implemented for algebraic numbers")

cutgeneratingfunctionology/igp/functions.sage

@@ -3197,15 +3197,15 @@ def is_all_QQ_fastpath(values):
             return False
     return True
 
-from sage.rings.number_field.number_field_element import is_NumberFieldElement
+from sage.rings.number_field.number_field_element_base import NumberFieldElement_base
 
 def is_all_the_same_number_field_fastpath(values):
     r"""
     This version does not try coercions and compares fields using ``is``, rather than their comparison operator.
     """
     number_field_seen = None
     for x in values:
-        if is_NumberFieldElement(x):
+        if isinstance(x, NumberFieldElement_base):
             if number_field_seen:
                 if number_field_seen is not x.parent():
                     return False
@@ -3259,7 +3259,7 @@ def is_QQ_linearly_independent(*numbers):
     if not is_all_the_same_number_field_fastpath(numbers):
         # try to coerce to common number field
         numbers = nice_field_values(numbers, RealNumberField)
-        if not is_NumberFieldElement(numbers[0]):
+        if not isinstance(numbers[0], NumberFieldElement_base):
             is_QQ, QQ_numbers = is_all_QQ(numbers)
             if is_QQ:
                 return False