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Moved all of `lib/llm/src/engines` to their own crates as e.g. `lib/engines/mistralrs`. This will allow publishing of the `dynamo-llm` crate as it won't have any github dependencies.

The only engines in dynamo-llm will be the demo `echo` ones.
Co-authored-by: Graham King <grahamk@nvidia.com>

Co-authored-by: Neelay Shah <neelays@nvidia.com>

Signed-off-by: hanweisen <hanweisen_yewu@cmss.chinamobile.com>

Co-authored-by: mabdulwahhab <mabdulwahhab@nvidia.com>

Co-authored-by: Ryan Olson <ryanolson@users.noreply.github.com>

Co-authored-by: hongkuanz <hongkuanz@nvidia.com>

Signed-off-by: Tianer Zhou <ezhoureal@gmail.com>

Put the arguments in a JSON file:
```
{
    "dtype": "half",
    "trust_remote_code": true
}
```

Pass it like this:
```
dynamo-run out=sglang ~/llm_models/Llama-3.2-3B-Instruct --extra-engine-args sglang_extra.json
```

Requested here https://github.com/ai-dynamo/dynamo/issues/290 (`dtype`) and here https://github.com/ai-dynamo/dynamo/issues/360 (`trust_remote_code`).