op-batcher: enforce Espresso network timeouts at one seam instead of per call site #501

Enforce timeouts at one seam instead of per call site. The submitter uses 3 of the SDK's 14 methods (SubmitTransaction, FetchTransactionByHash, FetchLatestBlockHeight); a thin wrapper applying NetworkTimeout inside those, plus the same bound inside batcherL1Adapter/batcherL2Adapter (which the streamer's reads already go through, so Peek gets covered too), fixes the whole unbounded-context class from my review and means a future call site can't forget the timeout. The ad-hoc networkTimeoutCtx blocks at individual call sites can then go.

Original discussion: #459 (comment)