[FEATURE] Add functions for Simulation-Based Calibration (SBC) analysis

[basantakhakurel]

Hi,

This PR introduces a new workflow for processign and visualizing Simulation-Based Calibration results for validating models implemented in RevBayes.

This new functionality is encapsulated in two new exported functions: processSBC() and plotSBC().

Summary of changes:

• processSBC(): A new function that reads the output directory of RevBayes validation analysis.
• plotSBC(): A new plotting function that creates ggplot objects that compare the observed coverage probability to the expected probability.
• Documentation: Both functions are documented with proper descriptions of parameters and runnable examples in the documentation.
• Dependency: coda package has been added to the DESCRIPTION file.
  This addition provides the model validation procedure directly within the RevGadgets ecosystem.

Additionally, I realized that the unit tests via GitHub Actions were failing during the installation of the ggtree package due to a version conflict with ggplot2.
A globally set R_BIOC_VERSION: 3.19 was forcing the jobs running to fetch incompatible packages from Bioconductor.

To resolve this and hopefully improve future stability, this PR:

• Removes the R_BIOC_VERSION override from the workflow file.
• Introduces a pkg.lock file to prevent this kind of 'dependency drift' from causing issues in the future.

I plan to write a detailed guide on troubleshooting these type of issues to the Developer Guide in a separate, follow-up PR.
EDIT: I managed to put it in the latest commit in this PR.

I hope this will be a useful contribution to the package.

[cmt2]

Thanks Basanta, looks great!