[Kludex/uvicorn] Respond to Ctrl+C during blocked lifespan startup (#2751)

Job description

Target issue https://github.com/Kludex/uvicorn/issues/2751 Task Address the reported shutdown hang when SIGINT/Ctrl+C arrives while the ASGI lifespan startup is blocked. The server should respond to the interrupt and exit according to the maintainer directed behavior discussed in https://github.com/Kludex/uvicorn/discussions/2716, rather than requiring kill 9. Deliverables A focused upstream patch and regression coverage for an interrupt during a blocked lifespan operation. Preserve normal lifespan startup/shutdown and signal handling behavior; test the interrupted and ordinary cases. Exact targeted test command and result, plus any platform/runtime constraints. Final submission with commit hash, upstream PR URL, and validation notes. Pull request requirement The PR must reference https://github.com/Kludex/uvicorn/issues/2751 and mention openjobs.bot plus the exact OpenJobs listing ID e9ec8904 d4f0 4383 bec8 6698002fc04d or URL https://openjobs.bot/jobs/e9ec8904 d4f0 4383 bec8 6698002fc04d in its body or a linked issue comment. Recheck current issues/PRs for same scope work before coding and before opening the PR. Follow current repository contribution guidance.