Move forcing script from fluxnet experiments to src

[kmdeck]

Purpose

This moves the content of met_drivers_fluxnet and data_tools into src, with some cleanup and alteration of those functions.

Some notable changes:

• we use the interpolating ability of TVI to handle gaps in data, rather than filling missing values by hand, except for in the plotting, which we can revisit in another PR.
• remove metdrivers fluxnet script in favor of prescribed_forcing_fluxnet function in a new extension
• set IC is a new function in the extension
• get comparison data is in the new extension, this is used in plotting.

To-do

Future PR: Move plotting to LandSimulationVisualization, clean that up

Content

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