Apply various clippy fixes

[Isona]

Apply cargo clippy and rust fmt recommendations.

There are 2 clippy suggestions left to apply:

1. Implementing default for HttpVerb - adding this broke the clap macro surrounding it. This is likely to need overhauling as part of updating Clap from 2 to 4
2. The variable parent_index is only used in recursion in the function listable_check