Add vllm bench [latency, throughput] CLI commands

[mgoin]

Was able to fully move benchmarks/benchmark_latency.py and benchmarks/benchmark_throughput.py into vllm bench latency and vllm bench throughput commands, respectively. I also added tests for all three latency/serve/throughput commands. In a followup PR I will move more functionality into serve that was left behind. We can also remove some of the utility files in benchmarks/ as they will be in the vllm package now. This should wait for a few vLLM releases imo

Tested manually and with CI smoke tests added:

vllm bench latency --model RedHatAI/Llama-4-Scout-17B-16E-Instruct-FP8-dynamic --max-model-len 8000 --tensor-parallel-size 2 --input-len 1000 --output-len 1000 --batch-size 1 --num-iters-warmup 5 --num-iters 5
vllm bench latency --model meta-llama/Llama-3.2-1B-Instruct 
vllm bench throughput --model meta-llama/Llama-3.2-1B-Instruct --input-len 32 --output-len 1 --enforce-eager

vllm serve meta-llama/Llama-3.2-1B-Instruct
vllm bench serve --model meta-llama/Llama-3.2-1B-Instruct

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[comaniac]

Given this PR mostly copies the code from benchmarks I mainly reviewed the dependencies and scope. Overall LGTM.