Enable @defer/incremental delivery on the owned-connection path

R429’s owned-connection path releases the pinned connection at operation completion, so a deferred fetcher running after the initial result would use a closed connection. The V0 stance is therefore that incremental delivery stays off: the owned factory never opts in, and GraphitronConnectionInstrumentation.beginExecuteOperation rejects an execution with incremental support enabled outright (pinned by ConnectionLifecycleExecutionTest). Enabling @defer/@stream under owned connections must own the connection-lifetime story: when release happens relative to deferred delivery, and how that composes with the tenant-keyed carrier’s lazy per-key acquisition. Session identity itself needs no per-fetcher story: the <sessionState> mount runs once at pin time as committed session state, so a late fetcher on a still-pinned connection sees it; the open question is purely when releaseAll (which unmounts) may run. Named as a follow-on in R429’s @defer section; this item is its tracking home now that the R429 spec is deleted.