Remove dependency on types-requests

[rouge8]

Please read this first

• Have you read the docs? Yes
• Have you searched for related issues? Yes, searched types-requests.

Describe the feature

types-requests should be a dev dependency, not a direct dependency of the package because it should have no effect at runtime. Additionally, the latest releases of requests include inline type hints: https://github.com/psf/requests/blob/HEAD/HISTORY.md#2340-2026-05-11 which means anyone using openai-agents gets a types-requests package that differs from the bundled type hints.

[scosemicolon]

A small packaging split that would make this safer:

• move types-requests out of runtime dependencies and into the dev/type-check dependency group
• keep requests as the only runtime dependency when it is actually imported at runtime
• add a packaging/import check that installs the wheel in a clean env and verifies pip show openai-agents no longer pulls types-requests
• if CI still needs stubs for older requests versions, pin them only in the type-check job rather than in the published package metadata

That would avoid forcing a possibly mismatched stub package into downstream environments now that recent requests releases include inline typing, while still keeping the SDK's own static checks reproducible.

[seratch]

Thanks for sharing this. requests 2.34 is pretty new, so we'd like to hold off removing types-requests at this moment.