Fix AstroCustomXcomBackend circular import issue (#1945)

When using AstroCustomXcomBackend and Python SDK 1.5, we were raising
the exception:

```
Traceback (most recent call last):
  File /usr/local/bin/airflow, line 5, in <module>
    from airflow.__main__ import main
  File /usr/local/lib/python3.9/site-packages/airflow/__init__.py, line 55, in <module>
    settings.initialize()
  File /usr/local/lib/python3.9/site-packages/airflow/settings.py, line 567, in initialize
    import_local_settings()
  File /usr/local/lib/python3.9/site-packages/airflow/settings.py, line 524, in import_local_settings
    import airflow_local_settings
  File /usr/local/airflow/airflow_local_settings.py, line 10, in <module>
    from airflow.models.baseoperator import BaseOperator
  File /usr/local/lib/python3.9/site-packages/airflow/models/baseoperator.py, line 75, in <module>
    from airflow.models.taskinstance import TaskInstance, clear_task_instances
  File /usr/local/lib/python3.9/site-packages/airflow/models/taskinstance.py, line 93, in <module>
    from airflow.models.xcom import XCOM_RETURN_KEY, LazyXComAccess, XCom
  File /usr/local/lib/python3.9/site-packages/airflow/models/xcom.py, line 835, in <module>
    XCom = resolve_xcom_backend()
  File /usr/local/lib/python3.9/site-packages/airflow/models/xcom.py, line 818, in resolve_xcom_backend
    clazz = conf.getimport(core, xcom_backend, fallback=fairflow.models.xcom.{BaseXCom.__name__})
  File /usr/local/lib/python3.9/site-packages/airflow/configuration.py, line 809, in getimport
    return import_string(full_qualified_path)
  File /usr/local/lib/python3.9/site-packages/airflow/utils/module_loading.py, line 33, in import_string
    module = import_module(module_path)
  File /usr/local/lib/python3.9/importlib/__init__.py, line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File /usr/local/lib/python3.9/site-packages/astro/custom_backend/astro_custom_backend.py, line 6, in <module>
    from astro.custom_backend.serializer import deserialize, serialize
  File /usr/local/lib/python3.9/site-packages/astro/custom_backend/serializer.py, line 12, in <module>
    if airflow.__version__ >= 2.3:
AttributeError: partially initialized module 'airflow' has no attribute '__version__' (most likely due to a circular import) 
```
Relates to: apache/airflow#31379
Closes: #1939

python-sdk/src/astro/custom_backend/serializer.py

@@ -5,21 +5,27 @@
 from json import JSONDecodeError
 from typing import Any
 
-import airflow
 import numpy as np
 import pandas
+import sqlalchemy
+from packaging import version
 
-if airflow.__version__ >= "2.3":
+try:
     from sqlalchemy.engine.row import LegacyRow as SQLAlcRow
-else:
+except ImportError:
     from sqlalchemy.engine.result import RowProxy as SQLAlcRow
 
+
 from astro.files import File
 from astro.table import Table, TempTable
 
 log = logging.getLogger("astro.utils.serializer")
 
 
+def is_newer_sqlalchemy():
+    return version(sqlalchemy.__version__) >= version.parse("1.4.0")
+
+
 def serialize(obj: Table | File | Any) -> dict | Any:  # noqa
     """
     Serialize astro SDK objects (tables, files and dataframes) into json safe dictionary
@@ -52,7 +58,7 @@ def serialize(obj: Table | File | Any) -> dict | Any:  # noqa
             "key_map": obj._keymap,  # skipcq PYL-W021
             "key_style": obj._key_style,  # skipcq PYL-W021
         }
-        if airflow.__version__ >= "2.3":
+        if is_newer_sqlalchemy():
             serialized_obj["data"] = obj._data  # skipcq PYL-W021
         return serialized_obj
 
@@ -90,7 +96,7 @@ def deserialize(obj: dict | str | list) -> Table | File | Any:  # noqa
             log.debug("Found file dictionary %s, will attempt to deserialize", obj)
             return _deserialize_file(obj)
         elif obj["class"] == "SQLAlcRow":
-            if airflow.__version__ >= "2.3":
+            if is_newer_sqlalchemy():
                 return SQLAlcRow(None, None, obj["key_map"], obj["key_style"], obj["data"])
             else:
                 return SQLAlcRow(None, None, obj["key_map"], obj["key_style"])