fix: timestamp dataset name if there's a collision

[nabinchha]

Closes: #74

[11:32:11] [INFO] 🎨 Creating Data Designer dataset
[11:32:11] [INFO] ✅ Validation passed
[11:32:11] [INFO] ⛓️ Sorting column configs into a Directed Acyclic Graph
[11:32:11] [INFO] 📂 Dataset path '/Users/nmulepati/Desktop/Work/DataDesigner/.scratch/artifacts/dataset' already exists. Dataset from this session
		             will be saved to '/Users/nmulepati/Desktop/Work/DataDesigner/.scratch/artifacts/dataset_11-25-2025_113211' instead.
[11:32:11] [INFO] 🩺 Running health checks for models...
[11:32:11] [INFO]   |-- 👀 Checking 'nvidia/nvidia-nemotron-nano-9b-v2' in provider named 'nvidia' for model alias 'nvidia-text'...
True
[11:32:12] [INFO]   |-- ✅ Passed!
[11:32:12] [INFO] ⏳ Processing batch 1 of 1
[11:32:12] [INFO] 🎲 Preparing samplers to generate 100 records across 1 columns
[11:32:12] [INFO] 📝 Preparing llm-text column generation
[11:32:12] [INFO]   |-- column name: 'greetings_completion_openai'
[11:32:12] [INFO]   |-- model config:
{
    "alias": "nvidia-text",
    "model": "nvidia/nvidia-nemotron-nano-9b-v2",
    "inference_parameters": {
        "temperature": 0.85,
        "top_p": 0.95,
        "max_tokens": null,
        "max_parallel_requests": 4,
        "timeout": null,
        "extra_body": null
    },
    "provider": "nvidia"
}