refactor: replace insecure custom downloader with Down::NetHttp

[alexskr]

refactor: replace insecure custom downloader with Down::NetHttp

• drop ftp support
• Harden repository copy path (OntologySubmission.copy_file_repository)
• Normalize src (accept Tempfile or String path)
• Sanitize destination filename (strip control/unsafe chars, trim/collapse spaces, remove leading dots, 255-char cap)

[codecov]

Codecov Report

❌ Patch coverage is 90.24390% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.66%. Comparing base (b12f205) to head (10c4e51).

Files with missing lines	Patch %	Lines
lib/ontologies_linked_data/utils/file.rb	88.00%	3 Missing ⚠️
...tologies_linked_data/models/ontology_submission.rb	93.75%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #260      +/-   ##
===========================================
+ Coverage    80.06%   80.66%   +0.60%     
===========================================
  Files           84       84              
  Lines         5873     5828      -45     
===========================================
- Hits          4702     4701       -1     
+ Misses        1171     1127      -44     

Flag	Coverage Δ
unittests	80.66% <90.24%> (+0.60%)	⬆️

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