Gather and pass routing data to t-route incrementally at each timestep

[PhilMiller]

For the sake of state saving, we want t-route to be responsible for ownership of all routing state. This avoids a potential need to save the entire history of nexus flows for the duration of the (potentially very long) run in order to pass it to t-route at the very end.

Changes

Testing

Notes

Todos

Checklist

• PR has an informative and human-readable title
• Changes are limited to a single goal (no scope creep)
• Code can be automatically merged (no conflicts)
• Code follows project standards (link if applicable)
• Passes all existing automated tests
• Any change in functionality is tested
• New functions are documented (with a description, list of inputs, and expected output)
• Placeholder code is flagged / future todos are captured in comments
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