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/records.rs

@@ -0,0 +1,84 @@
+use onspring::{OnspringClient, PagingRequest, QueryRecordsRequest, SaveRecordRequest};
+use std::collections::HashMap;
+
+#[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 field_id = std::env::var("TEST_TEXT_FIELD").expect("TEST_TEXT_FIELD is required");
+
+  let client = OnspringClient::builder(&api_key)
+    .base_url(&base_url)
+    .build();
+
+  // List records
+  let paging = PagingRequest {
+    page_number: 1,
+    page_size: 5,
+  };
+  let response = client
+    .list_records(app_id, Some(paging), None, None)
+    .await?;
+  println!("Total records: {:?}", response.total_records);
+
+  if let Some(items) = &response.items {
+    for record in items {
+      println!("  Record ID: {}", record.record_id);
+    }
+  }
+
+  // Create a record
+  let mut fields = HashMap::new();
+  fields.insert(field_id.clone(), serde_json::json!("Hello from Rust SDK"));
+
+  let request = SaveRecordRequest {
+    app_id,
+    record_id: None,
+    fields,
+  };
+
+  let saved = client.save_record(request).await?;
+  println!("\nCreated record with ID: {}", saved.id);
+
+  // Get the record back
+  let record = client.get_record(app_id, saved.id, None, None).await?;
+  println!(
+    "Fetched record: app_id={}, record_id={}",
+    record.app_id, record.record_id
+  );
+
+  // Update the record
+  let mut fields = HashMap::new();
+  fields.insert(field_id, serde_json::json!("Updated from Rust SDK"));
+
+  let update = SaveRecordRequest {
+    app_id,
+    record_id: Some(saved.id),
+    fields,
+  };
+  client.save_record(update).await?;
+  println!("Updated record {}", saved.id);
+
+  // Query records
+  let query = QueryRecordsRequest {
+    app_id,
+    filter: format!(
+      "{} contains 'Rust'",
+      std::env::var("TEST_TEXT_FIELD").unwrap()
+    ),
+    field_ids: None,
+    data_format: None,
+  };
+  let query_result = client.query_records(query, None).await?;
+  println!("\nQuery found {:?} records", query_result.total_records);
+
+  // Delete the record
+  client.delete_record(app_id, saved.id).await?;
+  println!("Deleted record {}", saved.id);
+
+  Ok(())
+}