refactor: implement new querying interface

[JabobKrauskopf]

This PR removes the old query engine and implements the new query engine as an interface in the querying.pyi. All current query engine usage was refactored to use the new interface.

It does not include the interface for control flow

Expected tests to fail:

• 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

[JabobKrauskopf]

Usage examples:

def query(node: NodeOperand):
    edges_to_treatment = node.outgoing_edges()
    edges_to_treatment.target_node().in_group("treatment")

    edges_to_outcome = node.outgoing_edges()
    edges_to_outcome.target_node().in_group("outcome")

    max_time_edge = edges_to_treatment.attribute("time").max()

    max_time_edge.less_than(edges_to_outcome.attribute("time"))


medrecord.select_nodes(query)

[LauraBoenchenLB]

Very cool new query engine! Can't wait to use it to build complex queries with 😎