Adding debug options to trtllm-build to visualize the TRT Network before Engine build

[Lokiiiiii]

Overview

This PR adds 2 new flags to trtllm-build to support debugging. --visualize-network dumps the finalized TRT Network as SVG files for visual analysis. --dry-run runs through all the steps except the Engine build and serialization which are typically the operations with the most overhead.

When used together, the TRT Network is dumped in ~10 secs for llama2-70B.

Testing

These changes have been manually tested for a few configurations of llama2.

Unit Tests

I can add more unit tests to this PR and fix existing unit tests if this basic design is acceptable.