Avoid memory leak warnings from pypdfium2 (#1902)

* Import `pypdfium2` early to ensure the `atexit` registered by `pypdfium2` is invoked after our `after_pipeline` method is.

Closes #1864

## By Submitting this PR I confirm:
- I am familiar with the [Contributing Guidelines](https://github.com/nv-morpheus/Morpheus/blob/main/docs/source/developer_guide/contributing.md).
- When the PR is ready for review, new or existing tests cover these changes.
- When the PR is ready for review, the documentation is up to date with these changes.

Authors:
  - David Gardner (https://github.com/dagardner-nv)

Approvers:
  - Michael Demoret (https://github.com/mdemoret-nv)

URL: #1902

examples/llm/cli.py

@@ -16,6 +16,10 @@
 import time
 
 import click
+# pypdfium2 utilizes an atexit handler to perform cleanup, importing here to ensure that handler is registered before
+# after_pipeline is, and thus is executed after after_pipeline is invoked. This avoids memory leak warnings at shutdown.
+# https://github.com/nv-morpheus/Morpheus/issues/1864
+import pypdfium2  # pylint: disable=unused-import # noqa: F401
 
 from llm.agents import run as run_agents
 from llm.completion import run as run_completion