feature - update gemini client to support proxy

[nihao]

• update gemini client to support proxy

    pub fn with_proxy(mut self, proxy_url: &str) -> Self {
        let proxy = reqwest::Proxy::all(proxy_url).expect("Proxy URL should be valid");
        self.http_client = reqwest::Client::builder()
            .proxy(proxy)
            .build()
            .expect("Gemini reqwest client should build");
        self
    }

[0xMochan]

Thanks for this PR. Is there a specific reason proxy URLs should be used only with Gemini, shouldn't this be available globally? We generally try to avoid PRs without associated issues so it would be best if there was a feature request issue made that describes this feature and why it's neccessary!

[nihao]

Each provider has an independent Client, and I am currently only using Gemini. We can define a trait with a default implementation for with_proxy for all providers if necessary.