Add snapshot tests for resolver (#5404)

## Summary

This PR adds some snapshot tests for the resolver based on executing
resolutions within a "mock" of the Airflow repo (that is: a folder that
contains a subset of the repo's files, but all empty, and with an
only-partially-complete virtual environment). It's intended to act as a
lightweight integration test, to enable us to test resolutions on a
"real" project without adding a dependency on Airflow itself.

crates/ruff_python_resolver/resources/test/airflow/README.md

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+# airflow
+
+This is a mock subset of the Airflow repository, used to test module resolution.

crates/ruff_python_resolver/resources/test/airflow/airflow/__init__.py

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+

crates/ruff_python_resolver/resources/test/airflow/airflow/api/__init__.py

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+

crates/ruff_python_resolver/resources/test/airflow/airflow/api/common/__init__.py

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+

crates/ruff_python_resolver/resources/test/airflow/airflow/api/common/mark_tasks.py

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+# Standard library.
+import os
+
+# First-party.
+from airflow.jobs.scheduler_job_runner import SchedulerJobRunner
+
+# Stub file.
+from airflow.compat.functools import cached_property
+
+# Namespace package.
+from airflow.providers.google.cloud.hooks.gcs import GCSHook
+
+# Third-party.
+from sqlalchemy.orm import Query

crates/ruff_python_resolver/resources/test/airflow/airflow/compat/__init__.py

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+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.

crates/ruff_python_resolver/resources/test/airflow/airflow/compat/functools.py

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+"""Empty file included to support filesystem-based resolver tests."""

crates/ruff_python_resolver/resources/test/airflow/airflow/compat/functools.pyi

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+"""Empty file included to support filesystem-based resolver tests."""

crates/ruff_python_resolver/resources/test/airflow/airflow/jobs/scheduler_job_runner.py

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+"""Empty file included to support filesystem-based resolver tests."""

crates/ruff_python_resolver/resources/test/airflow/airflow/providers/google/cloud/hooks/gcs.py

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+"""Empty file included to support filesystem-based resolver tests."""

crates/ruff_python_resolver/resources/test/airflow/venv/lib/python3.11/site-packages/sqlalchemy/__init__.py

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+

crates/ruff_python_resolver/resources/test/airflow/venv/lib/python3.11/site-packages/sqlalchemy/orm/base.py

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+"""Empty file included to support filesystem-based resolver tests."""

crates/ruff_python_resolver/resources/test/airflow/venv/lib/python3.11/site-packages/sqlalchemy/orm/dependency.py

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+"""Empty file included to support filesystem-based resolver tests."""

crates/ruff_python_resolver/resources/test/airflow/venv/lib/python3.11/site-packages/sqlalchemy/orm/query.py

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+"""Empty file included to support filesystem-based resolver tests."""