CSV Forcing Provider - enhanced error checking and cleanup

[PhilMiller]

The CSV Forcing provider is still in use, particularly for calibration use cases. I identified a number of cases in which it could currently be made to silently return bad data, thus leading to incorrect scientific results. This PR adds guard rails against those cases.

Additions

• .cpp file for the implementation of class CsvPerFeatureForcingProvider, with contents moved from the header

Changes

• Store name of forcing file from construction, so that it can be reported in later error messages
• Use stored file name in place of missing catchment ID variable when reporting errors
• Tighten checks for bad time inputs and arguments
• Enforce the limitation of the code that data record durations and request time steps are all exactly one hour
• Delete dead variables and code
• Improve const safety and copy-avoidance

Testing

Notes

• The one-hour timestep and record duration limitations might actually be problematic if used with some sources of forcing data. E.g. GFS data stretches to 3 hour intervals, and long-term forecasts may involve data or steps at 6-hour intervals. This PR does not enable any such uses, but rather ensures that they fail clearly rather than computing nonsensically.

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
• Project documentation has been updated (including the "Unreleased" section of the CHANGELOG)
• Reviewers requested with the Reviewers tool ➡️

[PhilMiller]

This fails in the unit test currently. Investigating.

[kyle-larkin]

This is fine, I think narrowing the time range on the unit tests as a follow on to get this merged would be sufficient.