feat(core): a cable carries one frame after the other, as in Java

Java's SimplexVerbindung sleeps a cable's delay with the port's buffer
locked: frames on one cable leave one after the other, and a frame shows
in the packet log when it leaves. The engine now queues a frame in the
output buffer until the one before has arrived (ethernetLinkDeparture).
Swift sends a cable's frames at once; the option swiftCables keeps that for
the Swift comparison, which goes on checking everything else trace by
trace.

With the queue, the Java comparisons match within 120 ms (was 200); a
state of the TCP stories within 250 ms, where the engine's calls block
one after the other.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/core/test/javaRun.ts

@@ -14,16 +14,17 @@
 //
 // Java runs on threads in real time, at the default speed of 90 % (55 ms a
 // cable, a round trip time of 2750 ms). Its gaps match the engine's within a
-// few milliseconds, except where a card sends two frames at once: Java's
-// cable carries one frame at a time (SimplexVerbindung sleeps the delay with
-// the port's buffer locked, and the sender waits), the engine's cable all of
-// them together — up to three cables' delay, measured. A gap may differ by
-// GAP_TOLERANCE_MILLISECONDS; a wrong round trip time (250 ms) may not.
+// few milliseconds; where they do not, it is Java's threads (a sender blocked
+// by a busy cable wakes late, up to some 110 ms measured), the log's lost
+// DISCOVER above, or a story whose calls the engine makes one after the
+// other. A gap may differ by GAP_TOLERANCE_MILLISECONDS; a wrong round trip
+// time (250 ms) may not. A cable carries one frame after the other in both
+// (engine.test.ts checks that: one cable's delay is below this tolerance).
 
 import { NetworkRuntimeEngine, TCP_FLAG, type EthernetFrame } from '../src/index.js';
 import { snapshotOf, type Scenario } from './scenario.js';
 
-export const GAP_TOLERANCE_MILLISECONDS = 200;
+export const GAP_TOLERANCE_MILLISECONDS = 120;
 const DUPLICATE_WINDOW_MILLISECONDS = 300;
 
 export interface JavaFrame {