Feat: Spam Ban: Also ban users who have left the server

[Asartea]

Because

#647

This PR

• Modifies the spam banning service to use guild.members.ban() for banning, which also allows banning user's who have left the server
• Modifies the rest of the code to account for this
• Slightly refactors some of the banning code
• Updates tests and snapshots

Issue

Closes #647

Additional Information

Pull Request Requirements

• I have thoroughly read and understand The Odin Project Contributing Guide
• The title of this PR follows the location of change: brief description of change format, e.g. Callbacks command: Update verbiage
• The Because section summarizes the reason for this PR
• The This PR section has a bullet point list describing the changes in this PR
• If this PR addresses an open issue, it is linked in the Issue section
• If applicable, I have ensured all tests related to any command files included in this PR pass, and/or all snapshots are up to date

[JustWaveThings]

Looks good to me. I pulled it down and ran it in my own server and tested it there as well. Thanks Asartea!