[16.0][IMP] rental_base_extension: post_init_hook for existing records

[eantones]

Summary

• When rental modules are installed on a database with existing sale orders, type_id, rental and can_sell_rental fields remain NULL because defaults/computes only apply to new records
• This causes errors when editing old quotations (Order Type radio buttons blank, attrs evaluation fails)
• Adds a post_init_hook that sets the correct defaults on existing records via SQL (xmlid resolved via ORM)

Test plan

• Install rental_base_extension on a database with existing sale orders
• Verify all orders have type_id set to "Normal Order"
• Verify all order lines have rental = False and can_sell_rental = False
• Open an old quotation and confirm no errors, Order Type shows "Pedido Normal"

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 44.41%. Comparing base (ec6499b) to head (ef90143).
⚠️ Report is 2 commits behind head on 16.0.

Additional details and impacted files

@@            Coverage Diff             @@
##             16.0     #885      +/-   ##
==========================================
+ Coverage   44.30%   44.41%   +0.11%     
==========================================
  Files         313      314       +1     
  Lines        6230     6243      +13     
  Branches      989      989              
==========================================
+ Hits         2760     2773      +13     
  Misses       3449     3449              
  Partials       21       21              

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