Clear up a series of small bugs and warnings

[RHammond2]

This PR address the following issues:

• Docs build failure
  • Brings the conf.py sidebar settings up to date with the current version of the sphinx book theme
  • Brings the myst-nb settings up to date with the current version of myst-nb and myst-parser
• File access error potentially resolved by closing out all logging handlers to close live file accessors
• Updates the Dinwoodie and IEA Task 26 examples
• Fixes inconsistencies in Metrics so that returned values are consistently pd.DataFrames, and not sometimes floats
• Fixes divide by zero error in task_completion_rate
• Fixes issue in project_fixed_costs where the inflation rate is only applied to the full years, and not the remainder months
• Minor documentation updates

Thanks, @akey7 for identifying some of these issues!

closes #36 closes #38