without-async

The asyncio primitives the rest of without is built from. It sits below the substrate and speaks only the standard library: every signature here mentions asyncio, collections.abc, and datetime types and nothing else, which is what lets a package take it without taking the stream vocabulary along.

• background_task starts a task on entry and cancels-then-awaits it on exit, so nothing leaks past the with block.
• timeout models "no limit" as None rather than as a sentinel float.
• limit_concurrency drives work from a source only while below the limit, so a lazy source is never advanced past it, over cancel_futures and as_async_iterator.
• Seconds and Milliseconds are counts, not durations: a boundary that carries whole units declares one instead of a timedelta it would silently truncate. These are the two symbols the package name does not cover; they sit here because every duration they carry is one something waits out.
• without_async.testing holds yield_once and resolved_next_turn, the two deterministic single-turn helpers a test reaches for when the code it waits on offers no signal of its own.

See the without-async guide (with the API reference) for the full surface.