Add None handling to sandbox/gateway/snapshot wait

[nadolskit]

Summary:

• Adds a guard on wait functions of sandbox/add gateway/waiting for pods
• The k8s watch api can yield None under misc conditions (such as network drops, timeouts, etc) causing 'NoneType' object is not subscriptable

Context:
as seen in our dev environment:

ERROR 2026-03-13 17:22:32,450 job_service [dispatch] sandbox error for 4a5ae8e3-adfe-4c1f-a2d3-760f115bba8a
Traceback (most recent call last):
  File "/app/packages/crow-service/crow_service/services/sandbox_client.py", line 384, in start
    await asyncio.to_thread(self._sync_client.start)
  File "/usr/local/lib/python3.12/asyncio/threads.py", line 25, in to_thread
    return await loop.run_in_executor(None, func_call)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/concurrent/futures/thread.py", line 59, in run
    result = self.fn(*self.args, **self.kwargs)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/app/packages/crow-service/crow_service/services/sandbox_client.py", line 170, in start
    SandboxClient.__enter__(self)  # noqa: PLC2801
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/app/.venv/lib/python3.12/site-packages/k8s_agent_sandbox/sandbox_client.py", line 343, in __enter__
    self._wait_for_sandbox_ready()
  File "/app/.venv/lib/python3.12/site-packages/k8s_agent_sandbox/trace_manager.py", line 178, in wrapper
    return func(self, *args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/app/.venv/lib/python3.12/site-packages/k8s_agent_sandbox/sandbox_client.py", line 198, in _wait_for_sandbox_ready
    if event["type"] in ["ADDED", "MODIFIED"]:
       ~~~~~^^^^^^^^
TypeError: 'NoneType' object is not subscriptable

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/app/packages/crow-service/crow_service/services/job_service.py", line 481, in dispatch_queued_job
    response: JSONResponse = await run_crow_job(
                             ^^^^^^^^^^^^^^^^^^^
  File "/app/packages/crow-service/crow_service/services/job_service.py", line 902, in run_crow_job
    await sandbox.start()
  File "/app/packages/crow-service/crow_service/services/sandbox_client.py", line 390, in start
    raise SandboxError(str(e)) from e
crow_service.services.sandbox_client.SandboxError: 'NoneType' object is not subscriptable

Resolves: #392

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• ✅ login: nadolskit / name: Tyler Nadolski (688988e, 6b6a32e)

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[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: aditya-shantanu, nadolskit
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