Inactivity Buffer and Gains command

[incinn]

• adds inactivity simulation output to check command showing the user how many days they can go inactive before falling below their rank xp requirement
• adds gains command showing a daily breakdown of xp gained
  • average xp/day value
  • median xp/day value
• adds gains command to core commands category on help output
• adds tests
• updates PR workflow to add a comment if the version check fails
• updates license information
• updates readme with new command

closes #230

[github-actions]

⚠️ Version hasn't been incremented (still 4.10.1). Consider bumping the version in this PR.