[FIX] stock_account: round SVL's value of incoming move

The SVL of in/out moves may be different because of rounding

To reproduce the issue:
(Need purchase,sale_management,stock)
1. In Settings, enable "Multi-Currencies"
2. Edit the USD currency:
    - Rounding factor: 1.0
3. Create a product category PC:
    - Costing Method: FIFO
4. Create a product P:
    - Type: Storable
    - Category: PC
5. Create a purchase order PO with one line:
    - Product: P
    - Quantity: 0.5
    - Unit Price: 3.0
    - Taxes: None
6. Confirm the PO and receive P
7. Create a sale order SO with 0.5 x P
8. Confirm the SO and deliver P
9. Inventory > Reporting > Inventory Valuation

Error: The quantity of P is zero but its total value is 0.50$

When receiving P, a SVL is created but does not round the value. So, we
have 0.5 x P in stock with a value equal to $1.50
Then, when deliver the product, the FIFO process is executed and create
a second SVL. However, this time the value is rounded:
https://github.com/odoo/odoo/blob/2e4fdcb84ba6375bb51fe71355168cebe2d922a0/addons/stock_account/models/product.py#L290


Therefore, the SVL of the out move has a value equal to $2. This
explains why, when checking the inventory valuation, the value is $-0.50

OPW-2724864

closes odoo/odoo#89743

X-original-commit: bf9b03a8
Signed-off-by: William Henrotin (whe) <whe@odoo.com>
Signed-off-by: Adrien Widart <awt@odoo.com>