Optimize: replace String with Cow<'_, str>

[RoDmitry]

Less String clones -> more performance 😊
Also Derive optimizations.

[RoDmitry]

@haydenhoang check it out. Does it look good?

[RoDmitry]

There is a problem which I have skipped, in OpenApi generation:

pub struct UpdateNlSearchModelParams<'p> {
    /// The ID of the NL search model to update
    pub model_id: Cow<'p, str>,
    /// The NL search model fields to update
    pub body: models::NlSearchModelCreateSchema, // missing <'p>
    pub _phantom: PhantomData<&'p ()>,
}

Somehow it thinks that models::NlSearchModelCreateSchema isPrimitiveType, maybe some mistake in openapi.yml.
And actually I don't even care about it. Fixable by hand 😏

[haydenhoang]

Hey @RoDmitry do you have any benchmark showing performance gain from replacing String with Cow<'_, str>?

Doing that make the code more complex and harder to maintain (lifetimes, phantom data), and I think the user might prefer the easy use of String if there is no significant performance gain.

[RoDmitry]

Benchmark of the clones? I don't think that's necessary. That's an obvious optimization. There will be significant performance gain, if you benchmark it. I don't want to, because I understand how slow memory allocations are.
The code is more complex, but not to the point that it's harder to maintain.

User will not be bothered by the lifetimes much. It's either local lifetime or 'static. Also lifetimes might be usable in other future optimizations like borrowing of slices or anything else.
String can be wrapped by Cow using Cow::from, or just using .into(), which is the replacement of .to_owned() in the current code, so a user will not care about it.

Although I agree that Cow<'_, str> does not look as solid as String especially if a user is a newbie to Rust.
In my codebase I have clones of big models::SearchParameters in loops, so it's very useful in my case.