Avoid extra_dejson in ADF and Synapse async hooks

[Vamsi-klu]

closes: #55728

What is the change?

The async paths in the Azure Data Factory and Synapse pipeline hooks stop reading conn.extra_dejson and parse extras with json.loads(conn.extra) instead. AzureSynapsePipelineAsyncHook.get_async_conn now fetches the connection through get_async_connection rather than the sync get_connection, and ADF refresh_conn closes the cached _async_conn before rebuilding it.

Why did I do it?

extra_dejson can call mask_secret, which does a sync send on the triggerer event loop and raises RuntimeError: You cannot use AsyncToSync in the same thread as an async event loop. The stack users see at execute_complete is that trigger error re-raised. This is the same leftover that #55179 fixed for MSGraph.

How did I do it?

In hooks/data_factory.py and hooks/synapse.py I swapped conn.extra_dejson for json.loads(conn.extra) if conn.extra else {} on the async paths only, and made refresh_conn await self.close(). The sync hooks keep extra_dejson so worker-side secret masking is unchanged.

What's the impact?

Deferrable ADF and Synapse pipeline runs stop crashing on the triggerer with the AsyncToSync error. Sync hooks and execute_complete behave exactly as before. Azure provider only.

What's the test plan?

New unit tests make extra_dejson raise the real AsyncToSync error and assert the async hooks still build their clients; they fail if extra_dejson comes back. test_refresh_conn now asserts the aio client gets closed. Reviewers can re-run the two touched test files or breeze testing providers-tests --test-type "Providers[microsoft.azure]"; provider CI covers the same.

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[Vamsi-klu]

Could you review the leftover extra_dejson and sync get_connection hops on the ADF and Synapse async hooks? This is the same AsyncToSync triggerer-loop failure as #55179, now in AzureDataFactoryAsyncHook.get_async_conn / provide_targeted_factory_async and AzureSynapsePipelineAsyncHook.get_async_conn. The question is whether json.loads(conn.extra) on the async path, and get_async_connection in the Synapse hook, is the right leftover fix, and whether leaving the sync hooks on extra_dejson is correct.

cc @dabla @eladkal @Lee-W

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Drafted-by: Cursor Grok 4.6 (no human review before posting)