Unnest nested types

[CBielstein]

Description

Several places in code have nested types. Examples of this include Packet.Type and Timestamp.Type. These files are hundreds of lines long and unnesting these types (e.g. to PacketType and TimestampType) would help break up long files and clarify the difference between a field on a packet and a type of packet.

Acceptance Criteria

• [x] Locate nested types in the code
• [x] Move them in to separate files
• [x] Ensure tests pass
• [x] Justify not unnesting in this issue or in the PR comments as appropriate

[CBielstein]

Potentially some options in Position.cs as well.