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::*`.

Cargo.toml

@@ -1,10 +1,13 @@
 [package]
-name = "onspring"
+name = "onspring-api-sdk-rust"
 version = "0.0.0"
 edition = "2021"
 description = "Rust SDK for the Onspring API"
 license = "MIT"
 
+[lib]
+name = "onspring"
+
 [dependencies]
 bytes = "1"
 reqwest = { version = "0.12", features = ["json", "multipart", "stream"] }