feat: add integration tests and runnable examples

Add 91 integration tests (all #[ignore]) mirroring the JavaScript SDK's
integration test suite. Tests cover all endpoints: ping, apps, fields,
records, files, lists, and reports with success, auth, access, and
not-found scenarios.

Add 7 runnable examples (cargo run --example <name>) for quick manual
smoke testing against a real Onspring instance.

Both use env vars (API_BASE_URL, SANDBOX_API_KEY, TEST_*) matching the
JavaScript SDK setup.

Also rename crate to onspring-api-sdk-rust with [lib] name = "onspring"
so imports remain `use onspring::*`.

examples/reports.rs

@@ -0,0 +1,56 @@
+use onspring::{OnspringClient, PagingRequest};
+
+#[tokio::main]
+async fn main() -> onspring::Result<()> {
+  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")
+    .expect("TEST_SURVEY_ID is required")
+    .parse()
+    .expect("TEST_SURVEY_ID must be an integer");
+
+  let client = OnspringClient::builder(&api_key)
+    .base_url(&base_url)
+    .build();
+
+  // List reports for an app
+  let paging = PagingRequest {
+    page_number: 1,
+    page_size: 10,
+  };
+  let response = client.list_reports(app_id, Some(paging)).await?;
+  println!("Total reports: {:?}", response.total_records);
+
+  if let Some(items) = &response.items {
+    for report in items {
+      println!(
+        "  Report: {} (id: {}, app_id: {})",
+        report.name.as_deref().unwrap_or("N/A"),
+        report.id,
+        report.app_id,
+      );
+    }
+
+    // Get report data for the first report
+    if let Some(first) = items.first() {
+      let data = client.get_report(first.id, None, None).await?;
+      println!(
+        "\nReport '{}' data:",
+        first.name.as_deref().unwrap_or("N/A")
+      );
+      println!("  Columns: {:?}", data.columns);
+
+      if let Some(rows) = &data.rows {
+        println!("  Rows: {}", rows.len());
+        for (i, row) in rows.iter().take(3).enumerate() {
+          println!(
+            "    Row {}: record_id={:?}, cells={:?}",
+            i, row.record_id, row.cells
+          );
+        }
+      }
+    }
+  }
+
+  Ok(())
+}