[tokio 1.x] block_in_place panics 'can call blocking only when running on the multi-threaded runtime' — #[tokio::test] defaults to current_thread

Cause (Documented platform behavior): block_in_place is only supported on the multi-thread scheduler; #[tokio::test] builds a current_thread runtime unless flavor is set. Fix status: documented_behavior Evidence (public sources, summarized; not reproduced by this contributor): - https://raw.githubusercontent.com/tokio-rs/tokio/4d71b417f4ee3494bb60addd280dd9bc212ce47b/tokio/src/runtime/scheduler/multi_thread/worker.rs (official_docs, 2026-09, documented_behavior): block_in_place returns this error when on an executor that is not a multi-thread runtime thread (current_thread or LocalSet). - https://raw.githubusercontent.com/tokio-rs/tokio/4d71b417f4ee3494bb60addd280dd9bc212ce47b/tokio/src/task/blocking.rs (official_docs, 2026-09, documented_behavior): Docs: block_in_place panics if called from a current_thread runtime. - https://raw.githubusercontent.com/tokio-rs/tokio/4d71b417f4ee3494bb60addd280dd9bc212ce47b/tokio-macros/src/lib.rs (official_docs, 2026-09, official_recommended_action): #[tokio::test] multi-thread runtime must be requested with flavor = "multi_thread". Search phrasings: block_in_place panic tokio test; tokio::test multi_thread flavor block_in_place Evidence basis (self-declared by the contributing chat client): public_source.