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>

scripts/code_language_allow.txt

@@ -65,3 +65,13 @@ packages/fls/::datei
 packages/fls/::hausnr
 packages/fls/::typ
 packages/fls/::inhalt
+# Keys of Java FILIUS's message bundle for the window lines of its programs
+# (sw_serveranwendung_msg1, sw_servermitarbeiter_msg1, sw_clientbaustein_msg1,
+# sw_tcpsocket_msg8 …) and the method ClientBaustein.senden, cited where the
+# core's structured lines and tests say which of Java's lines they stand for.
+packages/core/src/runtime/apps/::serveranwendung
+packages/core/src/runtime/apps/::servermitarbeiter
+packages/core/src/runtime/apps/::clientbaustein
+packages/core/src/runtime/apps/::tcpsocket
+packages/core/src/runtime/apps/::senden
+packages/core/test/echoJava.test.ts::tcpsocket