fix(quic-interop): bump multiconnect transfer timeout to 60s

After the handshake timeout bump and the faster PTO landed, the last
remaining flake was picoquic's handshakecorruption iter ~35: the
handshake recovers from 2-3 PTO rounds and smoothed_rtt is left at
~1s (RFC 9002 §5.2 takes the sample from the largest-acked packet's
SEND time, and that's the PTO retransmit, not the original).
post-handshake PTO is then 3s+, doubling. Three doublings under 30%
bit-flip eat 24s before the GET retransmit lands — 30s is a cliff.

60s gives the slow-recovery iterations real headroom. Total budget:
50 iters × ~3s typical = 150s, plus a few 60s outliers, comfortably
within the runner's 300s testcase budget.

Verified clean: aioquic, picoquic, quic-go each pass all 7 tests
(handshake, multiplexing, longrtt, transferloss, transfercorruption,
handshakeloss, handshakecorruption). 21/21.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

quic/interop/src/main/kotlin/com/vitorpamplona/quic/interop/runner/InteropClient.kt

@@ -72,7 +72,20 @@ private const val HANDSHAKE_TIMEOUT_SEC = 10L
 // per-iter transfer; the file is 1KB but its STREAM frames have
 // to land through the same lossy path.
 private const val MULTICONNECT_HANDSHAKE_TIMEOUT_SEC = 30L
-private const val MULTICONNECT_TRANSFER_TIMEOUT_SEC = 30L
+
+// Multiconnect transfer-side per-iter budget. Larger than the
+// handshake budget because once 1-RTT keys are up our smoothed_rtt
+// reflects the loss-recovery cost — RFC 9002 §5.2 takes the RTT
+// sample from the largest-acked packet's send time, and that's the
+// PTO-retransmit that finally landed, not the original send. So an
+// iteration whose handshake recovered after 2-3 PTO rounds will
+// have smoothed_rtt ~1s, which doubles the post-handshake PTO into
+// 3s+. Three doublings under 30% bit-flip can hit 24s before our
+// GET request is acked, so 30s is right on the cliff. 60s gives
+// the slow-recovery iterations real headroom; 50 iters × ~3s
+// average + a few slow ones × 60s still fits the runner's 300s
+// testcase budget.
+private const val MULTICONNECT_TRANSFER_TIMEOUT_SEC = 60L
 
 // Multiplexing generates ~hundreds-to-thousands of small files; download
 // throughput on Mac+Rosetta is dominated by Docker filesystem overhead