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- Mac doesn't have `pipe2` syscall so use plain `pipe`.
- rtnetlink isn't a dependency on mac so don't use the type

Previously we tokenized and counted tokens to stop when max tokens was reached. Now we let the mistral.rs engine do it which saves the extra tokenization step.

Also dynamo-run prints which engines are compiled in in help message, and some minor lint fixes.

"netlink" doesn't exist on Mac. We print the primary network interface to help multi-node setup, which is also unlikely on Mac.

- Any engine can take the name of a Hugging Face repository. It will be downloaded before calling the engine.

- The default engine (previously always mistralrs) depends on what is compiled in.

- Text can be piped in and will result in a single run of the model.

All of those together mean if you build with `--features vllm` you can do this and it will download the model and run it with vllm, answer your question, and exit:
```
echo "What is the capital of Costa Rica?"  | dynamo-run Qwen/Qwen2.5-3B-Instruct
```
Co-authored-by: Ryan McCormick <rmccormick@nvidia.com>

Command line arguments are passed to the python engine like this:
```
dynamo-run out=pystr:my_python_engine.py -- -n 42 --custom-arg Orange --yes
```

The python engine receives the arguments in `sys.argv`. The argument list will include some standard ones as well as anything after the `--`.

This input:
```
dynamo-run out=pystr:my_engine.py /opt/models/Llama-3.2-3B-Instruct/ --model-name llama_3.2 --tensor-parallel-size 4 -- -n 1
```

is read like this:
```
async def generate(request):
    .. as before ..

if __name__ == "__main__":
    print(f"MAIN: {sys.argv}")
```

and produces this output:
```
MAIN: ['my_engine.py', '--model-path', '/opt/models/Llama-3.2-3B-Instruct/', '--model-name', 'llama3.2', '--http-port', '8080', '--tensor-parallel-size', '4', '--base-gpu-id', '0', '--num-nodes', '1', '--node-rank', '0', '-n', '1']
```

This allows quick iteration on the engine setup. Note how the `-n` `1` is included. Flags `--leader-addr` and `--model-config` will also be added if provided to `dynamo-run`.

If the python file raises an exception we print it like Python would.

```
$ ./target/debug/dynamo-run in=http out=pystr:~/Temp/cn47/1_e.py --model-name test

Traceback (most recent call last):
  File "/home/graham/Temp/cn47/1_e.py", line 17, in generate
    raise MyException("The message")
1_e.MyException: The message
```

- Latest from repo, many improvements
- Support most of the OpenAI request features (temperature, top_p, etc)
- Download models from Hugging Face if necessary

For the `echo` and `pystr` engines we previously required the user to pass `--model-name <x>` so we would have a name for the model. If the input is HTTP we do need this to match on the users' JSON request.

If the input is Text we don't need a name. So if the input is Text and we don't already have a name for the model, give it one.

Co-authored-by: Biswa Panda <biswa.panda@gmail.com>