Fix stubtest errors

The generated type stubs in this repository are currently not correct, because the API uses PyO3-annotated Rust types from quil-rs and qcs-api-client-rust; in the type stubs, these types are imported from the PyO3 libraries generated in those repositories (quil and qcs_api_client_common), rather than from re-exports in the extension module in this repo. PyO3 types from different extension modules are inherently not the same type, so this makes the type stubs incorrect.

(In addition, as of 8/18/2026, there's an issue in pyo3-stub-gen that apparently prevents it from handling external imports correctly anyway; e.g. quil._quil.program.Program is used as program.Program, but the corresponding import is quil._quil.program.)

We have a bunch of stubtest errors in CI: https://github.com/rigetti/qcs-sdk-rust/actions/runs/18181235477/job/51757243866?pr=553#step:12:1233

Start with the stubtest errors in the linked CI job and the pyo3-stub-gen configuration or generated stubs. Trace how quil-rs and qcs-api-client-rust types are imported, including the external-import handling issue; done means the stubs reference this repository’s extension-module re-exports and the CI stubtest passes.