Fix clippy warnings

[thirteenowls]

Description

Fixed clippy warnings.

Motivation and Context

#483 (comment)

Dependencies

None.

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How has this been tested?

By running clippy and observing no warnings.

Is this change properly documented?

N/A

[thirteenowls]

Missed a couple, sorry. I'd only tested using the feature combinations I saw fail in CI.
clippy::assigning_clones will be moved to pedantic in the next release, and its current recommendation to use ToOwned::clone_into is incompatible with rspotify's MSRV, so I thought it'd be best to simply allow it for the time being.

[ramsayleung]

No worries, thanks for your contribution.