fix: load .env file in integration tests and examples

Add dotenvy to dev-dependencies and call dotenvy::dotenv().ok() in
the integration test common module and all examples so env vars can
be loaded from a .env file.

examples/reports.rs

@@ -2,6 +2,7 @@ use onspring::{OnspringClient, PagingRequest};
 
 #[tokio::main]
 async fn main() -> onspring::Result<()> {
+  dotenvy::dotenv().ok();
   let base_url = std::env::var("API_BASE_URL").expect("API_BASE_URL is required");
   let api_key = std::env::var("SANDBOX_API_KEY").expect("SANDBOX_API_KEY is required");
   let app_id: i32 = std::env::var("TEST_SURVEY_ID")