Split experiments from tests

The tests/ directory held 50 laboratory programs and no tests. They model
channels, run hundreds of repetitions and write CSV, PNG and reports;
calling that a test suite blocked introducing a real one, because any
pytest run would have collected the labs and re-executed every
experiment.

- move all 50 lab programs to experiments/ with git mv, preserving history
- rewrite the 38 cross-imports between labs from tests.labNNN to
  experiments.labNNN
- leave tests/ empty for actual fast checks of protocol/
- point quick_gate and the hook at the new layout and add experiments/ to
  the syntax sweep
- update the paths quoted in the Lab042 specification and the verifier
  agent definition

This also defuses the import-time work finding without touching 41 files:
the labs still create directories and write files on import, but nothing
imports them now except the gate, which does so deliberately.

Gate passes: syntax clean, protocol imports, 15 lab modules import, 2
functional suites run.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

experiments/lab004_protocol_module.py

@@ -0,0 +1,120 @@
+# -*- coding: utf-8 -*-
+"""
+Created on Fri Jul 10 17:19:11 2026
+
+@author: user
+"""
+
+"""
+Lab004. Проверка модуля protocol.packet.
+
+Проверяем:
+1. Формирование пакета.
+2. Разбор исправного пакета.
+3. Восстановление текста.
+4. Обнаружение повреждения CRC.
+"""
+
+from protocol.packet import (
+    CRCError,
+    HEADER_SIZE,
+    MESSAGE_TYPE_TEXT,
+    build_packet,
+    parse_packet,
+)
+
+
+# ============================================================
+# Формирование пакета
+# ============================================================
+
+message = "ПРИВЕТ SDR"
+payload = message.encode("utf-8")
+
+sequence_number = 7
+
+packet = build_packet(
+    payload=payload,
+    message_type=MESSAGE_TYPE_TEXT,
+    sequence_number=sequence_number,
+)
+
+
+print("Исходное сообщение:")
+print(message)
+
+print("\nСформированный пакет:")
+print(packet.hex(" "))
+
+print("\nРазмер пакета:")
+print(len(packet), "байт")
+
+
+# ============================================================
+# Разбор исправного пакета
+# ============================================================
+
+parsed_packet = parse_packet(packet)
+
+restored_message = parsed_packet.payload.decode("utf-8")
+
+
+print("\n--- Разобранный пакет ---")
+
+print("Версия:")
+print(parsed_packet.version)
+
+print("\nТип сообщения:")
+print(parsed_packet.message_type)
+
+print("\nПорядковый номер:")
+print(parsed_packet.sequence_number)
+
+print("\nПолезная нагрузка:")
+print(parsed_packet.payload)
+
+print("\nВосстановленное сообщение:")
+print(restored_message)
+
+
+assert parsed_packet.message_type == MESSAGE_TYPE_TEXT
+assert parsed_packet.sequence_number == sequence_number
+assert restored_message == message
+
+print("\nИсправный пакет успешно разобран.")
+
+
+# ============================================================
+# Повреждение одного бита
+# ============================================================
+
+corrupted_packet = bytearray(packet)
+
+# В строке "ПРИВЕТ SDR" буква S находится
+# по индексу 13 внутри полезной нагрузки.
+payload_byte_index = 13
+
+packet_byte_index = (
+    HEADER_SIZE + payload_byte_index
+)
+
+corrupted_packet[packet_byte_index] ^= 0x01
+
+
+print("\n--- Проверка повреждённого пакета ---")
+
+
+try:
+    parse_packet(corrupted_packet)
+
+except CRCError as error:
+    print("Повреждение обнаружено.")
+    print(error)
+
+else:
+    raise AssertionError(
+        "Ошибка: повреждённый пакет был принят как исправный"
+    )
+
+
+print("\nВсе проверки Lab004 успешно выполнены.")