RxJS SSE ownership: sseEvents$ and the caller-owned stream #75

Part of the audit remediation umbrella #67. Milestone 3. Severity: MEDIUM (decision). Requirement: ASYNC-21.

Current SDK behavior

sseEvents$ and typedSse$ (packages/rx/src/sse.ts:35,57-59) pass () => stream.close()
as the release argument of fromAsyncIterable. from-async-iterable.ts:103-108 runs
release on every termination: unsubscribe, end of source, and source error. ASYNC-21 says
the adapter "MUST NOT close the caller-owned source on any termination". pageItems$ and
pages$ pass no release. The Phase 8b checklist (:67) marks ASYNC-21 done with that clause
dropped from the gist. Neither §10 nor docs/deviations.md item 16 records the departure.

Expected behavior

One of the two, written down and tested:

• The adapter does not close the SseStream. The caller who built the stream calls close().
  Unsubscribing stops delivery but does not release the socket; the documentation says so.
• The adapter takes ownership and closes on every termination, and this is recorded as a
  deliberate deviation from ASYNC-21 in the Phase 8b ledger section and in
  docs/deviations.md.

Notes and leads

• The spec-faithful option is a one-line change and makes SSE match pagination. It moves a
  resource-leak risk onto the caller; document it in docs/sdk-documentation/ beside the
  for await guidance.
• The ownership-transfer option is more convenient for RxJS users and is what the code does
  today. The cost is a ledger row and a corrected checklist gist.
• Test either outcome: a subscription that is unsubscribed early, and a source that errors,
  asserting stream.close() call count.
• Any change: minor changeset for @dexpace/rx.