Added a decode+resize benchmark and cuda decoder

[ahmadsharif1]

1. Make the generate_readme_data.py script not regenerate the videos when the parent dir exists.
2. Add a benchmark column for "dataloader style" benchmark that measures throughput of a batch of videos that are decoded and resized.
3. Add a bar for cuda decoder which is nothing but torchcodec_public with device="cuda"

Benchmark results show cuda decoder is faster than CPU decoder at dataloader style benchmark.

[scotts]

Ideally we would also update the README description, as once this PR is merged, the chart is live. But we can also do that on a follow-up. That is, a 22-core Linux system with whatever kind of GPU.

[ahmadsharif1]

I tweaked the README.md file as well. Later on we can put the machine info in the chart itself so this doesn't have to be kept manually up-to-date.