Parallelize initContainer and main container image downloading

### 🚀 Feature Description and Motivation


Main container image is pulled after initContainer is done. If the initContainer runs time consuming work, there's an opportunity to download the image at the same time. In this case, it's faster that the workflow that pull image -> starts the engine -> pull model from remote.

### Use Case

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### Proposed Solution

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Start by locating the workflow that pulls the initContainer and main container images, then trace how the engine starts and the model is fetched. Define how image downloads can overlap without changing container startup ordering, and verify that the resulting workflow preserves the intended engine and model initialization behavior.

Written by the indexing model from the issue text.