feat: limit thread number to 1 when HDD is detected

[Integral-Tech]

On HDD, multi-threaded du won't provide any performance benefit over the single-threaded one. Therefore, when HDD is detected on one of the files, limit the thread number to 1.

Fixes #257

[KSXGitHub]

Thanks for your contribution. I have some requests and questions.

[KSXGitHub]

In addition to my request at #269 (comment), I also have more suggestions for improvement.

[KSXGitHub]

Before merging this, I need to try rewriting the dependency injections in the tests from passing functions to using a trait, like so:

pub trait Api {
    type Disk: ?Sized;
    fn get_disk_kind(&self, disk: &Self::Disk) -> DiskKind;
    fn get_mount_point(&self, disk: &Self::Disk) -> &Path;
    fn canonicalize(&self, path: &Path) -> io::Result<PathBuf>;
}

pub struct RealApi; // would implement real APIs

#[cfg(test)]
pub struct TestApi { /* ... */ } // would implement mocked APIs

Whilst I do not request you to implement this for me, you're welcomed to try if you are feeling generous enough. If you do not do it, then I will do this when I have free time.

[Integral-Tech]

Before merging this, I need to try rewriting the dependency injections in the tests from passing functions to using a trait, like so:

pub trait Api {
    type Disk: ?Sized;
    fn get_disk_kind(&self, disk: &Self::Disk) -> DiskKind;
    fn get_mount_point(&self, disk: &Self::Disk) -> &Path;
    fn canonicalize(&self, path: &Path) -> io::Result<PathBuf>;
}

pub struct RealApi; // would implement real APIs

#[cfg(test)]
pub struct TestApi { /* ... */ } // would implement mocked APIs

Whilst I do not request you to implement this for me, you're welcomed to try if you are feeling generous enough. If you do not do it, then I will do this when I have free time.

However, while any_path_is_in_hdd() needs all three closures, path_is_in_hdd() only needs two of them

[KSXGitHub]

However, while any_path_is_in_hdd() needs all three closures, path_is_in_hdd() only needs two of them

It's just an internal trait, not a user-facing public trait, so we don't need to make it modular. As for code simplicity, we are not passing any closures, we are passing a single instance of TestApi or RealApi.

I feel that the names I chose are somewhat horrible though. If you have better names, feel free to use them.

[KSXGitHub]

v0.11.0 has been released.