feat: implement automated reporting and visualization layer

[ayushman1210]

Description

Here's a breakdown of what I worked on:

• Updating the plotting functions: I refactored the old metric_timeseries_plot.R, metric_scatter_plot.R, and metric_residual_plot.R functions so they can easily consume the data.frame or data.table outputs straight from the run_benchmark() pipeline. I also took the opportunity to clean up the ggplot2 aesthetics (better themes, removing hardcoded date limitations, adding reference lines, etc.).
• Quarto report template: I created a new Validation_report.qmd template in inst/reports/. This generates a nice HTML scorecard (ILAMB-style) that compiles all our computed metrics alongside the plots.
• Reporting wrapper: I added generate_validation_report.R, which acts as a wrapper to render the Quarto template automatically at the end of a benchmark run.
• Testing: Added some basic tests in test-visualization.R to make sure the plots render correctly and the wrapper function handles missing templates gracefully.

Types of changes

• New feature (non-breaking change which adds functionality)

Fixes #4037

[divine7022]

solid work! thanks for putting this together
the bigger picture, ryt now this is plotting layer. and 4037 is validation report, and the job of a validation report is to answer two questions "is the model good enough ?" and "where does it fail ?". a stack of pretty panels doesn't answer either. the upgrades I am trying to asking are what turn this from "here are some plots" into "here's whether the model passes, and where it doesn't" none of it is hard and you have already got the pieces in.

and consolidate one off plot_time_series into these, it is not touched here. either fold it in or spin quick follow up