Clippy and typo fixes

[Ununoctium117]

Summary

• Fixes a bunch of clippy warnings
• Removes the accidentally-committed .DS_Store mac files
• Fixes the error handling for the unimplemented /escalate history subcommand. Old behavior was to not respond to the command at all; new behavior is:

which is the same as all the other unimplemented commands.

What kind of change does this PR introduce? (check at least one)

• Bugfix
• Feature
• Code style update
• Refactor
• Docs
• Build-related changes
• Other, please describe:

Does this PR introduce a breaking change? (check one)

• Yes
• No

If yes, please describe the impact and migration path for existing applications:

The PR fulfills these requirements:

• When resolving a specific issue, it's referenced in the PR's title (e.g. fix #xxx[,#xxx], where "xxx" is the issue number)

If adding a new feature, the PR's description includes:

• A convincing reason for adding this feature
• Related documents have been updated
• Related tests have been updated

To avoid wasting your time, it's best to open a feature request issue first and wait for approval before working on it.