feat(format): format does not specify an element type for list

### Describe the enhancement requested

While LIST itself is specified in format spec (protobuf), the element type does not specified anyhow and serialization the protobuf will result in just "list". But in C++ implementation it is `list`, for example, `list`.

### Component(s)

Format

Start by comparing the protobuf format specification's LIST definition with the C++ implementation's list representation. Check the issue discussion for the intended serialized form; done means the format specifies the element type consistently and serialization matches it.

Written by the indexing model from the issue text.