feat: add type narrowing to interface

[JabobKrauskopf]

This PR adds type narrowing operations to the interface

usability example:

Medrecord node attributes with mixed data types (non comparable)

def query(node: NodeOperand):
    node.attribute("value").max().less_than(5)

# Throws Error because of mixed data types with hint to use narrowing operation
medrecord.select_nodes(query)

def query(node: NodeOperand):
    value_attribute = node.attribute("value")
    value_attribute.is_int()
    value_attribute.max().less_than(5)

# Doesn't throw error
medrecord.select_nodes(query)

Expected tests to fail (same as in the previous PR):

• medmodels/medrecord/tests/test_builder.py
• medmodels/medrecord/tests/test_datatype.py
• medmodels/medrecord/tests/test_indexers.py
• medmodels/medrecord/tests/test_medrecord.py
• medmodels/medrecord/tests/test_overview.py
• medmodels/medrecord/tests/test_schema.py
• medmodels/treatment_effect/matching/tests/test_classic_distance_models.py
• medmodels/treatment_effect/matching/tests/test_metrics.py
• medmodels/treatment_effect/matching/tests/test_propensity_score.py
• medmodels/treatment_effect/tests/test_continuous_estimators.py
• medmodels/treatment_effect/tests/test_temporal_analysis.py
• medmodels/treatment_effect/tests/test_treatment_effect.py