* feat(http-request): add stream option and response metadata to downloads

Add stream option to httpRequest — resolves with HttpResponse immediately
after headers arrive, leaving rawResponse unconsumed for piping to files.

Refactor httpDownloadAttempt to use httpRequestAttempt with stream: true,
eliminating ~120 lines of duplicated HTTP plumbing (redirect handling,
protocol selection, error enrichment).

Add headers, ok, status, and statusText to HttpDownloadResult so callers
can inspect response metadata after streaming downloads.

* chore(release): 5.15.0