[FIX] partner_credit_limit: fix error `OverflowError: date value out of range`

[edy1192]

1. [FIX] partner_credit_limit: fix error OverflowError: date value out of range

   • Since the grace_payment_days field is a float, in some cases the user can set really high values (> 999999) which causes the traceback OverflowError: date value out of range.
   • Since that field is used for date operations in the debit_credit_maturity method of theres.partner model.

2. [FIX] partner_credit_limit: Add = to the validation condition

• There is data demo with the value of the grace_payment_days field set to 999999, that value must be included.

• Improve message that is displayed to the user when the constraint is executed, to show the value that is trying to save.

[edy1192]

Hi @luisg123v @moylop260

Cherry pick is done.

Regards.

[moylop260]

Thank you!