Adds quite a lot of Clippy lints which fit with my
personal taste for how pesde's codebase should
look like. Stylistic lints are mostly warns, and
behavioural lints are mostly denied.
Instead, we use the `default` serde attribute
to deserialize the index as `DEFAULT_INDEX_NAME`
if it is not present. This removes a lot of
redundancy around the codebase about getting
the index name.
