Audit: a gateway 502 on a relay broadcast releases the submission guard (Sherlock 159) #581

Tracking issue for Sherlock #159 (Low/Info), targeted at v0.10.6.

The privacy paymaster client read every non-2xx status as a refusal from the relay. Through the STRK20 gateway, a 502 means the gateway's own 25s upstream deadline expired, five seconds inside the wallet's 30s one. A relay that forwarded paymaster_executeTransaction but replied slowly therefore released the maturity submitting guard, and the next private action could broadcast a second time.

Fix: on a broadcast, treat a 5xx as an unknown outcome and keep a 4xx as a refusal. Set the wallet deadline below the gateway's. Have the gateway answer 504 on an upstream timeout and pass a relay's own 4xx through.