Improve simulator functionality

[Modularius]

Summary of changes

1. Changed unwraps to expects in build_messages.rs
2. Changed send_trace_message to send_digitiser_trace_message and integrated edits in send_messages.rs, simulation.rs, engine.rs and others.
3. Added Trace struct for channel traces in event_lists.rs and refactored
4. Added IntConstant and TextConstant types
5. Added EnsureDelayMs action
6. Improved error handling

Instruction for review/testing

General code review as the simulator was successfully tested in the pipeline.

[DanNixon]

I don't like the amount of unwrap and expect. Now that we have a standard for how error handling should happen I would like new and refactored code to use it (arguably it is of less concern for the simulator but I see a lot of the same elsewhere, anything related to tracing for example).

[Modularius]

There were considerably more unwraps than I realised. I've replaced them with anyhows (they inform the user of invalid JSON), and all remaining excepts should be impossible. The remaining unwraps are all part of test modules.

[DanNixon]

I've replaced them with anyhows (they inform the user of invalid JSON)

See https://github.com/STFC-ICD-Research-and-Design/supermusr-data-pipeline/blob/main/docs/style.md#crab-error-handling-rules, anyhow outside of the return type of main() is prohibited.