Apply MVC to pseudopotential uploader widget

[edan-bainglass]

This PR refactors the uploader widget to its own module and converts it to MVC. All is updated accordingly, including tests.

[codecov]

Codecov Report

❌ Patch coverage is 92.45283% with 12 lines in your changes missing coverage. Please review.
✅ Project coverage is 72.45%. Comparing base (e39dd4c) to head (1de6e6a).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...p/configuration/advanced/pseudos/uploader/model.py	85.71%	5 Missing ⚠️
...lab_qe/app/configuration/advanced/pseudos/utils.py	88.57%	4 Missing ⚠️
...onfiguration/advanced/pseudos/uploader/uploader.py	95.38%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1359      +/-   ##
==========================================
+ Coverage   72.38%   72.45%   +0.07%     
==========================================
  Files          99      103       +4     
  Lines        7166     7188      +22     
==========================================
+ Hits         5187     5208      +21     
- Misses       1979     1980       +1     

Flag	Coverage Δ
python-3.11	72.45% <92.45%> (+0.08%)	⬆️
python-3.9	72.47% <92.45%> (+0.05%)	⬆️

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[AndresOrtegaGuerrero]

LGTM!