Gather example hydrographs from HEC-RAS models

[thwllms]

To develop a reliable method for identifying stable vs. unstable hydrographs, we're going to need a lot of example data, especially from HEC-RAS models, since that's our primary target.

Some examples from an FFRD model are included in the repo already under tests/data/. We're going to need more.

We need a variety of:

• Hydrograph types (flow vs. stage)
• Human-labeled stability (stable vs. unstable)
• Magnitudes (i.e., max flow)
• Timesteps (minutes, hours, etc.)
• Sources (mesh cells/faces, reference lines, ...)

Hydrographs should be stored in CSV format, with an ISO-formatted datetime column and a value column. Organize in the repo based on whether they are considered by a human modeler to be stable or unstable.