Support top-level import for VLMRun class

[spillai]

This change correctly updates the import path. However, the need for this change highlights a potential improvement in the library's API design for better developer experience. A more user-friendly approach would be to allow importing VLMRun directly from the top-level vlmrun package. You could enable this by adding from .client import VLMRun to vlmrun/__init__.py. This would allow users to write from vlmrun import VLMRun, simplifying usage.

Originally posted by @gemini-code-assist[bot] in #129