fix: update return type in product model methods

Updated the getFieldValue and getFieldValueByLocale methods' return type in src/QUI/ERP/Products/Product/Model.php. Now these methods can return int, float, string, array, or null. Also simplified the exception statements.

mentioned in commit de59db8d

merged

This MR is included in version 2.5.2

The release is available on GitLab release.

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