#1767 sycl: add STRATA_DOORBELL_NOCHECK to skip the payload wait (debug only)

Description

## Summary
Adds an opt-in `STRATA_DOORBELL_NOCHECK` env switch: when set, `doorbell_wait_payload` trusts the ring and skips the payload-checksum wait. It exists because on this build **both** in-engine profilers fail before they can measure anything — `STRATA_VERIFY_EAGER=1` and `STRATA_VERIFY_PROFILE=1` both error in the verify window at layer 0 with `rang but its payload never arrived whole` (verify.cpp) — so the stage profiler cannot run. With the switch, the host-timed stage table prints.

## Dependency
**This PR is stacked on #1602** (`intel-sycl-handshake`): it modifies `doorbell_wait_payload`, which #1602 adds. The branch therefore contains #1602's commits; only the last commit (`sycl: add STRATA_DOORBELL_NOCHECK...`) is new. Merge after #1602, or cherry-pick that one commit once #1602 lands.

## Extra Notes
Debug/profile only. With it set, the CPU expert pool can read a stale payload and the output may be wrong — the exact race the checksum catches. It is inert when unset (a single `getenv`), so it has no effect on a normal run. It is the smallest way to unblock profiling on the SYCL path; the underlying eager-path payload failure is a separate, deeper issue and is not fixed here.