feat: Part #1 - New processing step to calculate/get split partitions
Part of https://github.com/huggingface/datasets-server/issues/1087
Given a chunk size and split row number, this job runner will generate partitions for a split.
Part of this code was already introduced in https://github.com/huggingface/datasets-server/pull/1213 but maybe is better to separate the PR in one for "partitions" calculation and another to add the new granularity logic.

Sample output cache having a chunk_size=50:
```
{
   "num_rows": 150,
   "partitions": [
                  {
                        "dataset": "dataset_ok",
                        "config": "config_ok",
                        "split": "split_ok",
                        "partition": "0-99",
                    },
                    {
                        "dataset": "dataset_ok",
                        "config": "config_ok",
                        "split": "split_ok",
                        "partition": "100-150",
                    },     
  ]
}
```
                    
feat: Part #1 - New processing step to calculate/get split partitions: Part of https://github.com/huggingface/datasets-server/issues/1087
Given a chunk size and split row number, this job runner will generate partitions for a split.
Part of this code was already introduced in https://github.com/huggingface/datasets-server/pull/1213 but maybe is better to separate the PR in one for "partitions" calculation and another to add the new granularity logic.

Sample output cache having a chunk_size=50:
```
{
   "num_rows": 150,
   "partitions": [
                  {
                        "dataset": "dataset_ok",
                        "config": "config_ok",
                        "split": "split_ok",
                        "partition": "0-99",
                    },
                    {
                        "dataset": "dataset_ok",
                        "config": "config_ok",
                        "split": "split_ok",
                        "partition": "100-150",
                    },     
  ]
}
```
                    