dag-cbor-derive should not assume a length while decoding

[dvc94ch]

[molekilla]

describe this one, seems to be in gen.rs ?

[wngr]

This is about being more liberal in what we accept when parsing, see for example https://github.com/ipfs-rust/libipld/blob/d92d261f4831f943ab243aa215d871a5734e8d89/dag-cbor-derive/src/gen.rs#L239-L241 and https://github.com/ipfs-rust/libipld/blob/d92d261f4831f943ab243aa215d871a5734e8d89/dag-cbor-derive/src/gen.rs#L298-L300