Fixing flaky test test_cli_can_build_and_search_index by retrying

[jamesbraza]

We can see from this CI run that test_cli_can_build_and_search_index flaked in build_index with a zlib.error:

  |   File "/home/runner/work/paper-qa/paper-qa/tests/test_cli.py", line 79, in test_cli_can_build_and_search_index
  |     build_index(index_name, stub_data_dir, settings)
  |   File "/home/runner/work/paper-qa/paper-qa/paperqa/agents/__init__.py", line 141, in build_index
  |     return get_loop().run_until_complete(get_directory_index(settings=settings))
  |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |   File "/home/runner/.local/share/uv/python/cpython-3.12.8-linux-x86_64-gnu/lib/python3.12/asyncio/base_events.py", line 686, in run_until_complete
  |     return future.result()
  |            ^^^^^^^^^^^^^^^
  |   File "/home/runner/work/paper-qa/paper-qa/paperqa/agents/search.py", line 674, in get_directory_index
  |     async with anyio.create_task_group() as tg:
  |                ^^^^^^^^^^^^^^^^^^^^^^^^^
  |   File "/home/runner/work/paper-qa/paper-qa/.venv/lib/python3.12/site-packages/anyio/_backends/_asyncio.py", line 767, in __aexit__
  |     raise BaseExceptionGroup(
  | ExceptionGroup: unhandled errors in a TaskGroup (1 sub-exception)
  +-+---------------- 1 ----------------
    | Traceback (most recent call last):
    |   File "/home/runner/work/paper-qa/paper-qa/paperqa/agents/search.py", line 476, in process_file
    |     if not await search_index.filecheck(filename=file_location):
    |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |   File "/home/runner/work/paper-qa/paper-qa/paperqa/agents/search.py", line 263, in filecheck
    |     index_files = await self.index_files
    |                   ^^^^^^^^^^^^^^^^^^^^^^
    |   File "/home/runner/work/paper-qa/paper-qa/paperqa/agents/search.py", line 252, in index_files
    |     zlib.decompress(content)
    | zlib.error: Error -5 while decompressing data: incomplete or truncated stream
    +------------------------------------

I am not entirely sure why this zlib.error happened, but this change is a first step in figuring it out. If the zlib.error happens across 3 retries, then we know there's deeper more going on.