[ADD] field_float_nullable: New field type float that supports NULL v…

[samirGuesmi]

New field type float that supports NULL values instead of defaulting to 0.0

In standard Odoo, fields.Float does not support distinguishing between 0.0 and NULL (i.e., an unset value). By default, if a float field is left empty in the UI, it is stored as 0.0 in the database. The goal is to allow users and developers to identify whether a float field has been filled in or not — something that cannot be reliably determined when 0.0 is used by default. The module also integrates fully with Odoo’s UI (form views, list views, export, custom filters

[samirGuesmi]

Thanks @sbidoul for the review! I've applied the suggested changes.

[OCA-git-bot]

This PR has the approved label and has been created more than 5 days ago. It should therefore be ready to merge by a maintainer (or a PSC member if the concerned addon has no declared maintainer). 🤖

[samirGuesmi]

Thans @sbidoul and @AnizR for the review. here is the updated version.