[18.0][IMP] purchase_manual_currency / purchase_stock_manual_currency: refactor to use standard currency_rate

[Saran440]

Refactor code manual_currency

• delete is_manual, currency_diff because they are not used
• delete total_company_currency since the standard field amount_total_cc already exists
• Replace manual_currency_rate with the standard currency_rate
• Update test script
• Reuse standard logic instead of introducing new custom logic

This PR is an improvement based on #2839

cc @TheerayutEncoder @AndreuOForgeFlow @HviorForgeFlow What do you think about this refactor?

[TheerayutEncoder]

Does it mean we cannot edit currency rate on PO, so what the purpose of this module?

[Saran440]

@TheerayutEncoder The currency_rate field already exists in the standard Purchase Order but is hidden.

This module simply exposes that field and allows users to edit it when using manual currency.
The computation still relies on the standard currency_rate logic instead of introducing a custom rate field.

[TheerayutEncoder]

@TheerayutEncoder The currency_rate field already exists in the standard Purchase Order but is hidden.

This module simply exposes that field and allows users to edit it when using manual currency. The computation still relies on the standard currency_rate logic instead of introducing a custom rate field.

Oh, I see it, so I think the way you did it is good. 👍

[HviorForgeFlow]

I think you've done a great job simplifying those legacy custom fields, would it be required a migration script to don't break existing instances using this module, at least historical data?

[Saran440]

@HviorForgeFlow Thank you for your advice. I added migration script and change version to 18.0.2.0.0 (purchase_manual_currency) and 18.0.1.0.1 (purchase_stock_manual_currency)
Can you check please?