feat: add macro attr with_extensions

[niklasad1]

Follow-up on #1306

Let's add on option to use Extensions in the API or not because it may be annoying to just mark it as used and would be nice not to break the previous API for existing users.

#[rpc(client, server)]
pub trait Rpc {
        // legacy
	#[method(name = "foo"])
	async fn async_method(&self, param_a: u8, param_b: String) -> u16>;

        // with extensions
	#[method(name = "with_ext", with_extensions)]
	async fn f(&self) -> bool;
}

impl RpcServer for () {
	async fn async_method(&self, param_a: u8, param_b: String) -> u16 {
            12
        }

	// NOTE: ext is injected here in the API
        async fn f(&self, ext: &Extensions: b: String) -> {
             ext.get::<u32>().is_ok()
        }
}

[jsdw]

Looks great to me; the attribute works well :)

[pkhry]

can you collapse the if into else if following the recommendation from clippy, otherwise LGTM

[mudlee]

Nice work! May I ask when it'll approximately be released? :)

[niklasad1]

Nice work! May I ask when it'll approximately be released? :)

We are "hoping" to get a new release out tomorrow