Ckhrysze/elixir cbor struct to array encoding

[ckhrysze]

Current behavior

The only struct encoding option is as an object

Proposed changes

Add an additional option to allow a struct to be serialized as a list.

#6614

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[polvorin]

This looks good, thanks for adding the tests 👍 .
Just a request, on the :struct case, we didn't require fields to be contiguously defined, that is a struct with fields numbers 1,2 and 4 is fine (no field # 3). Here, for the :struct_values case, we do expect them to be all defined (with a special case for letting the 0 to not be defined). I didn't had this in mind, but I think it's fine, that means unused fields (for example after an update where such a field is not used anymore) will still need to be defined as term() | nil. That actually has the benefit that we will be reminded we are wasting space there until we change the schema on all parties involved.

The request is, could you add a comment/doc about this on the :struct_values case please?. And maybe check that at compile time when using the Plugin too.