feat: Cache model and engine downloads so users can restart download

[freelerobot]

Problem:

1. cortex run trt/onnx model
2. wait for download
3. 10 minutes in, something might happen, internet drops/windows goes to sleep, etc.
4. Lose entire download progress.
5. Sadness

Happened for me 2/3 times for larger model folders

Suggested solution

• cache downloads, host a mirror, open to better suggestions

[freelerobot]

Related issues:

• bug: Model corruption during download leads to loading failure #1139
• bug: cortex pull from hf times out #1017
• bug: Download models/engine failed cause api server stop #1010
• feat: Add pause functionality to model downloader jan#3519

Related discussion:
#1129

[dan-menlo]

Linking this to main issue #1077