Rename `parallelism/_concurrent_futures_primes.py` ->
`concurrent_futures_primes.py` so the example-runner
(`test_docs_examples.py`) stops skipping it (leading `_` =
excluded) and CI finally exercises the `concurrent.futures`
baseline we compare against in the new parallelism guide.
Deats,
- keep the original executor code verbatim in a sync
`check_primes()` fn for clean docs excerpting,
- add module docstring + zero-arg `async def main()` +
`trio.run(main)` guard per the runner conventions.
(this patch was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code
Gud Boi