fix: ID type definition of Contact model

[gekkedev]

From what I observed, this is a string (serialized format, user@server). If there are exceptions where it is actually a WID object, let me know and I'll adapt this PR.

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[gekkedev]

I might have been wrong on this:
client.getMessages(chatId) returns messages where the sender attribute is a Contact object. The attribute id is a WID, not a serialized string. In wa-js this is also defined as WID: https://github.com/wppconnect-team/wa-js/blob/4df7fee17ed071b461e2da28d8e6c9e7592c9739/src/whatsapp/models/ContactModel.ts#L28
However, I'm pretty sure I had a use case where it was a serialized string (need to find out when exactly for reproduction).
It could be, that the type of id depends on which methods we use to get a Contact object. 🤔

@icleitoncosta what is the desired state here?

1. A union type for both possibilities? string | WID
2. wa-js deserializing if necessary to always provide a WID
3. wa-js serializing if necessary to always provide a string