stream: align Readable.toWeb termination with eos - #62394

PR-URL: #62394
Reviewed-By: Mattias Buelens <mattias@buelens.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

PR-URL: nodejs#62394
Reviewed-By: Mattias Buelens <mattias@buelens.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

PR-URL: #62394
Backport-PR-URL: #64675
Reviewed-By: Mattias Buelens <mattias@buelens.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

newReadableStreamFromStreamReadable watched its source with a plain
eos(stream, cb), which for a Duplex settles only once both sides are
done. The readable half of Duplex.toWeb() (and Readable.toWeb() over any
Duplex) therefore never reported done for a source whose readable side
had ended while its writable side stayed open: a read() issued after the
EOF hung until the writer was closed, which for a half-open socket whose
peer has sent FIN may never happen. Watch with { writable: false }, as
upstream does since v26.3.0 (nodejs/node#62394), so the ReadableStream
mirrors the readable side only. The writable half keeps watching the
whole Duplex, so writer.close() still settles after the readable side
has ended, matching upstream's Writable.toWeb.

The suite's pin of the old coupling is replaced by one asserting that
the EOF read resolves while the writable side is open and that the
writable half keeps working afterwards.

Compatibility: no flag. The only observable change is that a read()
which previously stayed pending until the writable side finished now
resolves with done; no read that previously settled changes its result,
and non-Duplex sources are unaffected since the option is a no-op for a
stream with no writable side.