feat(core): programs' threads, and FILIUS' echo server and generic client after Java, measured against Java

Programs run as generators that yield what they wait for (threads.ts); the
engine resumes them after every event. TCP connect, send, receive, accept
and name resolution exist as such steps; the blocking calls wrap them.
EchoRun records eight stories in Java FILIUS, frames, tables and each
program's window lines; echoJava.test.ts plays them card by card. Not
taken from Java: a connection without a route hangs for ever; a server
switched off leaves its connections' last FIN unanswered.

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

packages/core/test/scenarios/echo-java-notConnected.java.json

@@ -0,0 +1,49 @@
+{
+  "frames": {
+    "00000000-0000-0000-0000-000000000101": [],
+    "00000000-0000-0000-0000-000000000102": [],
+    "00000000-0000-0000-0000-000000000103": []
+  },
+  "rows": {
+    "00000000-0000-0000-0000-000000000101": [],
+    "00000000-0000-0000-0000-000000000102": [],
+    "00000000-0000-0000-0000-000000000103": []
+  },
+  "layeredRows": {
+    "00000000-0000-0000-0000-000000000101": [],
+    "00000000-0000-0000-0000-000000000102": [],
+    "00000000-0000-0000-0000-000000000103": []
+  },
+  "events": [
+    [
+      208,
+      "server",
+      "null"
+    ],
+    [
+      209,
+      "client",
+      "null"
+    ],
+    [
+      210,
+      "other",
+      "null"
+    ],
+    [
+      500,
+      "client",
+      "call senden Hallo"
+    ],
+    [
+      500,
+      "client",
+      "Fehler beim Verbindungsaufbau"
+    ],
+    [
+      500,
+      "client",
+      "returned senden"
+    ]
+  ]
+}