Dataset size and numberOfFiles becomes incorrect when dataset is created with initial values before OrigDatablock creation

Summary

The current implementation updates the dataset size incrementally when a new OrigDatablock is created:

    const createOrigDatablock: CreateOrigDatablockDto = {
      ...createDatasetOrigDatablockDto,
      datasetId: pid,
      ownerGroup: dataset.ownerGroup,
      accessGroups: dataset.accessGroups,
      instrumentGroup: dataset.instrumentGroup,
    };
    const datablock =
      await this.origDatablocksService.create(createOrigDatablock);

    const updateDatasetDto: PartialUpdateDatasetObsoleteDto = {
      size: dataset.size + datablock.size,
      numberOfFiles: dataset.numberOfFiles + datablock.dataFileList.length,
    };
    await this.datasetsService.findByIdAndUpdate(dataset.pid, updateDatasetDto);

This assumes that dataset.size and dataset.numberOfFiles always represent the sum of existing OrigDatablocks.

However, users can create a dataset with a predefined size and numberOfFiles before any OrigDatablock is created. When the first OrigDatablock is later added, the dataset values are incremented on top of the existing values, resulting in incorrect totals.

Steps to Reproduce

Create dataset

/api/v3/datasets
{
 ...otherfileds,
 size: 1000,
 numberOfFiles: 2
}

Create origDatablock

api/v3/datasets/:pid/origdatablocks
{
  ...otherfields,
   "dataFileList": [
    {
      "path": "string/string",
      "size": 1111,
      "time": "2026-03-04T09:37:02.960Z",
      "chk": "teststring",
    }
  ],

}

Current Behaviour

Fetch created dataset

api/v3/datasets/:pid

{
 ...otherfields,
 size: 2111,
 numberOfFiles:3
}

Expected Behaviour

Fetch created dataset

api/v3/datasets/:pid

{
 ...otherfields,
 size: 1111,
 numberOfFiles:1
}

Extra Details

Provide all the relevant details related to this issues. Include screenshot, wireframes and mockups if helpful.

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Start at the /api/v3/datasets/:pid/origdatablocks flow, especially origDatablocksService.create and datasetsService.findByIdAndUpdate. Trace how the dataset's initial size and numberOfFiles are combined with the first OrigDatablock, then verify the dataset response after creating the dataset with initial values and adding one OrigDatablock. Done means the returned totals match the OrigDatablocks rather than double-counting the initial values.