Finish adding tests for Itch Messages

[markwinter]

It's pretty essential that all of the Itch message parsing has tests to ensure they're correct and any mistakes or typos are caught.

This means testing both the Parse<MessageType> method, and the Bytes() method for each message type.

• [x] IPO Quotation
• [x] LULD Collar
• [x] MWCB Level
• [ ] MWCB Status
• [x] NOII
• [ ] Operational Halt
• [x] Order Add
• [x] Order Add Attributed
• [x] Order Cancel
• [x] Order Delete
• [x] Order Executed
• [x] Order Executed Price
• [x] Order Replace
• [x] Participant Position
• [x] Reg Sho
• [ ] RPII
• [x] Stock Directory
• [x] System Event
• [ ] Trade Broken
• [x] Trade Cross
• [x] Trade Non-Cross
• [x] Trading Action
• [ ] Direct Listing