Move examples/qualcomm out from under the torch namespace (#5400)

Summary:
The code under examples/... is a proxy for user code, and users should never declare code under the `torch::` or `executorch::` namespaces.

Move this code under the `example::` namespace to make it more clear that users should use their own namespaces when writing code like this.

Pull Request resolved: https://github.com/pytorch/executorch/pull/5400

Test Plan:
- Built using the instructions at https://github.com/pytorch/executorch/blob/main/examples/qualcomm/README.md
- test-llama-runner-qnn-linux CI job succeeded

Reviewed By: shoumikhin

Differential Revision: D62969111

Pulled By: dbort

fbshipit-source-id: 9ec27528dd85f60d8c538d54ce6ddf621e63cf52