feat(deps): upgrade pyattest and cbor2

[subpath]

Summary

• Bumps pyattest 1.0.2 -> 1.0.5, cbor2 5.7.0 -> 6.1.3.
• Unblocks the cbor2 6.x bump (chore(deps): bump cbor2 from 5.7.0 to 6.1.3 #207): pyattest 1.0.2 imports cbor2's C extension from a path removed in 6.x. 1.0.5 fixes it.
• pyattest 1.0.5 made Attestation.verify() a coroutine, updated verify_attest() for that.

Threading

• run_in_threadpool(attestation.verify) (old code, unchanged) -> runs but verifies nothing: constructs the coroutine in the thread, never drives it.
• Can't drop run_in_threadpool either: verify() is CPU-bound, so awaiting it directly blocks the event loop for every concurrent request.
• I think the best option is: run_in_threadpool(asyncio.run, attestation.verify()).

Benchmark: real verify_attest(), main vs this branch

400 concurrent calls, 3 runs each, DB write and GCS cert download mocked:

	Throughput (req/s)
main	603 / 589 / 634 (avg 609)
this branch	670 / 697 / 704 (avg 690)

~13% faster, no regressions.

[noahpodgurski]

Nice! 🚀