Lint for unused `[dependencies]`

### What it does

Detect unused dependencies and suggest removing them

### Advantage

- Faster builds
- False positives if done in rustc

### Drawbacks

- Complicated

### Example

```toml
[package]
name = "libc"

[dependencies]
clap = "4"
```

Could be written as:

```toml
[package]
name = "libc"

[dependencies]
```
(since `libc` doesn't use `clap`)
