Fixed length encoding of CBOR maps

[DhanusML]

During serialization, most of the maps in this crate are initialized
as serializer.serialize_map(None). This causes ciborium to serialize
the maps using indefinite length encoding. Hence deterministic
encoding requirements cannot be met. The CoSERV data format,
which derives many data types from CoRIM, requires CBOR definite
length encoding to be used (at least for query). Initializing the maps
(at least the ones used in CoSERV) with number of elements would
enable a CoSERV implementation using definitions from this crate to
comply with the specifications.

[setrofim]

Partially resolived by #46

CoSWID is still TODO