fix: accept empty arrays as null in Jackson deserialization

[pheizx]

Issue:

Cannot deserialize value of type `java.lang.String` from Array value (token `JsonToken.START_ARRAY`) at [Source: UNKNOWN; byte offset: #UNKNOWN] (through reference chain: io.facturapi.models.SearchResult["data"]->java.util.ArrayList[0]->io.facturapi.models.Invoice["items"]->java.util.ArrayList[0]->io.facturapi.models.InvoiceItem["property_tax_account"])

Fix:

This change handles an API response inconsistency where a field expected as a String can arrive as an empty array ([]).
Without this setting, Jackson throws a deserialization error for paths like InvoiceItem.property_tax_account.
By enabling DeserializationFeature.ACCEPT_EMPTY_ARRAY_AS_NULL_OBJECT, empty arrays are treated as null, preventing runtime parsing failures.

[javorosas]

Gracias por reportar el problema. La causa es que property_tax_account es un arreglo en V2; lo corregimos tipándolo como List en #10, con cobertura para arreglos vacíos y no vacíos. Cerramos este PR para evitar habilitar una tolerancia global de Jackson que ocultaría otros contratos inválidos.