Add scaling to tqdm bar when downloading files

[Rexhaif]

Changes proposed in this pull request:

• Adds unit scaling to Tqdm bar when it is used to track file downloading progress

Rationale:

Seeing million-like numbers in the tqdm bar when downloading large files is quite non-informative. I think that scaled units will be way more useful, as we see them daily while downloading files in the browser of checking connectivity speed on speedtest. Fortunately, tqdm has scaling features that convert numbers to their scaled variants like 12304556B -> 12,3MB.

That is used in other libraries, which deal with pretrained models, for example huggingface/transformers.

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[epwalsh]

Thanks @Rexhaif, this is great!