Feature Request: Allow injecting a custom reqwest::Client into WorkOS

[max-zheng]

Problem

WorkOsBuilder::build() always creates its own reqwest::Client internally:

let client = reqwest::Client::builder()
    .user_agent(concat!("workos-rust/", env!("CARGO_PKG_VERSION")))
    .build()
    .unwrap();

There's no way to pass in an existing reqwest::Client. This means applications that already have a configured client (with custom timeouts, connection pools, TLS settings, etc.) end up with two independent connection pools to api.workos.com.

Proposed Solution

Add a client method to WorkOsBuilder:

impl<'a> WorkOsBuilder<'a> {
    pub fn client(mut self, client: reqwest::Client) -> Self {
        self.client = Some(client);
        self
    }

    pub fn build(self) -> WorkOs {
        let client = self.client.unwrap_or_else(|| {
            reqwest::Client::builder()
                .user_agent(concat!("workos-rust/", env!("CARGO_PKG_VERSION")))
                .build()
                .unwrap()
        });
        // ...
    }
}

This is backwards-compatible — existing callers that don't set a client get the same default behavior.

Use Case

We wrap the WorkOS SDK in a client that also makes direct HTTP calls for operations not yet in the SDK (e.g., resend_invitation). Being able to share a single reqwest::Client would eliminate the duplicate connection pool.