Initialize `Client` with custom HTTP client, config, and backoff

[GabrielBianconi]

Initializing a Client with a custom HTTP client always requires first creating a useless reqwest::Client in Client::with_config.

This adds a bit of useless overhead due to reqwest's TLS/DNS functionality, which can be non-trivial for certain low-latency applications.

Would you be open to adding an additional method along the lines of?

impl<C: Config> Client<C> {
    /// Create client with your own HTTP client, config, and backoff 
    pub fn build(http_client: reqwest::Client, config: C, backoff: backoff::ExponentialBackoff) -> Self {
        Self {
            http_client,
            config,
            backoff,
        }
    }

...

[64bit]

Thank you for detailed description. Definitely open to it, PR is welcome!

I'm curious what happens with TLS/DNS on creating a new reqwest client?

[GabrielBianconi]

Great, just sent a PR #197.

During initialization, among other things, a reqwest client seems to initialize its TLS backend ref. In certain scenarios (at least for me: tiny VM with shared core + legacy backend), this seems to take a non-trivial amount of time. I observed ~30ms earlier this week. And with the current async-openai implementation, it wasn't possible to easily circumvent this dummy initialization.

Thanks!

[64bit]

I see, thank you for sharing!