Newtype is not defaulting to transparent and is wrapping with an array

[gpeacock]

Problem

Given a newtype struct wrapping a HashMap:

pub struct MyStruct(pub HashMap<String, ByteBuf>);

The library is incorrectly serializing it as a 1-element array containing a map (CBOR major type 4), rather than transparently as just the map itself (CBOR major type 5).

Before fix:

• CBOR output: [129, 162, ...] = 0x81 (array with 1 element) + 0xA2 (map with 2 entries)
• Major type: 4 (array) ❌

Expected:

• CBOR output: [162, ...] = 0xA2 (map with 2 entries)
• Major type: 5 (map) ✓