docs: clarify close ownership when a recovery step turns a Success into a Failure

[OmarAlJarrah]

Problem

The recovery-aware ResponsePipeline lets a step transform a ResponseOutcome.Success into a Failure (e.g. status-to-typed-exception mapping) or substitute a different Success. The original successful Response holds an open transport connection / body stream, but until now nothing documented who is responsible for closing it on that transform path. The actual behavior was easy to misread: it is tempting to assume the pipeline drains/closes any response it stops surfacing.

Actual behavior (now documented)

The ResponsePipeline closes the in-hand Success response on exactly one path: when a step throws while holding it. Both the success-path (applyResponseSteps) and the recovery chain (invokeRecovery) close-before-propagate and attach any close error to the step's throwable as suppressed.

It does not close the response when a step is handed a Success and deliberately returns a different outcome — a Success → Failure transform or a substitute Success. The pipeline never observes the dropped response, so the step that performs the transform owns closing the response it discards (outcome.response.close() before returning the replacement), or the connection leaks. The Failure(t1) → Failure(t2) "Replace" path carries no response, so there is nothing to close there.

Change

Documentation only:

• ResponseRecoveryStep KDoc — new "Close ownership when discarding a Success" section.
• ResponsePipeline KDoc — new "Close ownership of a discarded Success response" section describing the throw-only close path.
• docs/pipelines.md — matching subsection under the ResponsePipeline description.

No code behavior changes; :sdk-core compile, ktlint, detekt, and apiCheck pass.

Closes #110