[16.0][IMP] rental_base_extension, sale_rental_extension: remove parent translations from PO files

[eantones]

Summary

• Remove translations belonging to parent OCA modules (rental_base, sale_rental) from the NuoBiT extension modules' PO files
• Keep only strings truly introduced by each extension module (new fields, selections, actions, menus, views, JS strings, reports)
• Add .pot files exported from Odoo as ground truth reference
• Parent module translations will be managed via Weblate

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 44.30%. Comparing base (419ffde) to head (77f6562).
⚠️ Report is 3 commits behind head on 16.0.

Additional details and impacted files

@@           Coverage Diff           @@
##             16.0     #869   +/-   ##
=======================================
  Coverage   44.30%   44.30%           
=======================================
  Files         313      313           
  Lines        6230     6230           
  Branches      989      989           
=======================================
  Hits         2760     2760           
  Misses       3449     3449           
  Partials       21       21           

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