Fix for single file native upload: directory path gets lost

[bnavigator]

When uploading a single file with a directory label, this gets lost in the native upload:

╭────────────── DVUploader ──────────────╮
│ Server: https://darus.uni-stuttgart.de │
│ PID: doi:10.18419/DARUS-6027           │
│ Files: 1                               │
╰────────────────────────────────────────╯
🔎 Checking dataset files
┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┳━━━━━━━━┳━━━━━━━━┓
┃ File                                                   ┃ Status ┃ Action ┃
┡━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━╇━━━━━━━━╇━━━━━━━━┩
│ SOF-DWG-MM-1260.0.00 R01 Reference Mirror Assembly.pdf │ New    │ Upload │
└────────────────────────────────────────────────────────┴────────┴────────┘

⚠  Direct upload not supported. Falling back to Native API.

🚀 Uploading files

DEBUG: file=File(filepath='ta-library/1000 Optical Assembly/1200 Secondary Mirror Assembly/1260 SM Reference Mirror SMRM/_DWG/SOF-DWG-MM-1260.0.00 R01 Reference Mirror
Assembly.pdf', handler=None, description='SOF-DWG-MM-1260.0.00, Document Iteration No. 1 (Max: 1)', directory_label='1000 Optical Assembly/1200 Secondary Mirror Assembly/1260 SM
Reference Mirror SMRM/_DWG', mimeType='application/octet-stream', categories=['Lifecycle State: Released', 'TA Level 1: OA', 'TA Level 0: TA', 'TA Level 3: SMRM', 'Drawing', 'TA
Level 2: SMA', 'Company: Astrium', 'Document Iteration: Most Recent'], restrict=True, checksum_type=<ChecksumTypes.MD5: ('MD5', <built-in function openssl_md5>)>,
storageIdentifier=None, file_name='SOF-DWG-MM-1260.0.00 R01 Reference Mirror Assembly.pdf', checksum=Checksum(type='MD5', value=None), file_id=None, tab_ingest=True,
to_replace=False)
DEBUG: json_data={'description': 'SOF-DWG-MM-1260.0.00, Document Iteration No. 1 (Max: 1)', 'categories': ['Lifecycle State: Released', 'TA Level 1: OA', 'TA Level 0: TA', 'TA Level
3: SMRM', 'Drawing', 'TA Level 2: SMA', 'Company: Astrium', 'Document Iteration: Most Recent'], 'restrict': True}
(
    'File 1000 Optical Assembly/1200 Secondary Mirror Assembly/1260 SM Reference Mirror SMRM/_DWG/SOF-DWG-MM-1260.0.00 R01 Reference Mirror Assembly.pdf not found in Dataverse
repository.',
    'This may be due to the file not being uploaded to the repository:'
)
SOF-DWG-MM-1260.0.00 R01 Reference Mirror Assembly.pdf ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 100% 0:00:00

✅ Upload complete

[JR-1991]

@bnavigator thanks for the PR! Tested it locally and it works perfect. Code looks great as well. Merging!