Not Equals (!=) Expressions

[slincoln-aiq]

This PR introduces using "not equals" expressions, such as !=, over the not_token for the convert_condition_field_eq_val() method and all the convert_condition_field_eq_val_*() methods.

This is done by using a context manager inside convert_condition_field_eq_val() . The convert_condition_field_eq_val() method will first check if:

1. The current condition has a parent, grandparent, ...etc ConditionNOT
2. The convert_not_as_not_eq class flag is True

The resulting bool value is passed to the context manager as the use_negated_expressions arg, the the method carries on like normal. If use_negated_expressions is True, the following expressions will be temporarily swapped with their 'not equals' counterpart while converting the condition using the convert_condition_field_eq_val_*() methods, then swapped back after the conversion is complete:

self.eq_expression = self.not_eq_expression
self.re_expression = self.not_re_expression
self.cidr_expression = self.not_cidr_expression
self.startswith_expression = self.not_startswith_expression
self.case_sensitive_startswith_expression = self.case_sensitive_not_startswith_expression
self.endswith_expression = self.not_endswith_expression
self.case_sensitive_endswith_expression = self.case_sensitive_not_endswith_expression
self.contains_expression = self.not_contains_expression
self.case_sensitive_contains_expression = self.case_sensitive_not_contains_expression

I have also added tests for this new logic in the test_conversion_base file.

To use this functionality, the backend developer should set the not equals expressions listed above in their backend, and set convert_not_as_not_eq = True.

Here is an example of a passing test using the current logic with the not_token:

def test_convert_not(test_backend):
    assert (
        test_backend.convert(
            SigmaCollection.from_yaml(
                """
            title: Test
            status: test
            logsource:
                category: test_category
                product: test_product
            detection:
                sel:
                    fieldA: value1
                condition: not sel
        """
            )
        )
        == ['not mappedA="value1"']
    )

vs using the new not_eq logic:

def test_convert_not_as_not_eq(test_backend, monkeypatch):
   """Test that NOT conditions are converted using not_eq expressions when convert_not_as_not_eq is True"""
   monkeypatch.setattr(test_backend, "convert_not_as_not_eq", True)
   monkeypatch.setattr(test_backend, "not_eq_token", "!=")
   monkeypatch.setattr(test_backend, "not_eq_expression", "{field}{backend.not_eq_token}{value}")
   assert (
       test_backend.convert(
           SigmaCollection.from_yaml(
               """
           title: Test
           status: test
           logsource:
               category: test_category
               product: test_product
           detection:
               sel:
                   fieldA: value1
               condition: not sel
       """
           )
       )
       == ['mappedA!="value1"']
   )