test(fly-app): add unit, integration, and e2e test coverage

- Pure unit tests for parse_cursor (None, valid, malformed, negative
  ledger) and serialize_raw (None, valid JSON inline, invalid JSON).
- DB-backed HTTP integration tests using actix_web::test::init_service
  against a real Postgres: wasms list grouping and channel resolution,
  wasm-by-version, 404s, limit/cursor validation, contracts JOIN across
  registered+deployed+wasms, and registries ordering.
- End-to-end test that loads registry-turbo-v4.yaml, replays each
  transform_3_* SQL over the real Soroban fixtures in
  test/fixtures/soroban-events-real/, and asserts the resulting rows
  surface correctly through /v1/registries, /v1/contracts, and
  /v1/wasms. Flipping the root contract id in the pipeline YAML makes
  the sub-registry filter drop to zero rows, failing this suite.

DB-gated tests skip silently when TEST_DATABASE_URL is unset; e2e
additionally requires the real fixtures directory to be populated.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: willemneal

fly-app/Cargo.lock

@@ -10,3 +10,11 @@ serde_json = "1"
 chrono = { version = "0.4", features = ["serde"] }
 sqlx = { version = "0.8", features = ["runtime-tokio", "postgres", "tls-rustls", "chrono"] }
 tokio = { version = "1", features = ["full"] }
+
+[dev-dependencies]
+# Integration tests that touch the shared Postgres test DB use `#[serial]`
+# so they don't race each other on TRUNCATE between tests.
+serial_test = "3"
+# e2e test loads registry-turbo-v4.yaml to pull the pipeline transform SQL
+# and replay it against Postgres before hitting the HTTP layer.
+serde_yaml_ng = "0.10"