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/lab002_bit_corruption.py

@@ -0,0 +1,153 @@
+"""
+Lab002, часть 2.
+Повреждение одного бита пакета без контроля целостности.
+
+Цель:
+1. Сформировать цифровой пакет.
+2. Намеренно изменить один бит полезной нагрузки.
+3. Разобрать повреждённый пакет.
+4. Убедиться, что без CRC повреждение не обнаруживается.
+"""
+
+import struct
+
+
+# ============================================================
+# Константы протокола
+# ============================================================
+
+SYNC_WORD = 0xAA55
+PROTOCOL_VERSION = 1
+MESSAGE_TYPE_TEXT = 1
+
+HEADER_FORMAT = ">HBBHH"
+
+
+# ============================================================
+# Формирование исходного пакета
+# ============================================================
+
+message = "ПРИВЕТ SDR"
+payload = message.encode("utf-8")
+
+sequence_number = 1
+message_type = MESSAGE_TYPE_TEXT
+payload_length = len(payload)
+
+header = struct.pack(
+    HEADER_FORMAT,
+    SYNC_WORD,
+    PROTOCOL_VERSION,
+    message_type,
+    sequence_number,
+    payload_length,
+)
+
+packet = header + payload
+
+
+print("Исходное сообщение:")
+print(message)
+
+print("\nИсходный пакет:")
+print(packet.hex(" "))
+
+
+# ============================================================
+# Имитация повреждения пакета
+# ============================================================
+
+# bytes нельзя изменять напрямую.
+# Поэтому преобразуем пакет в изменяемый массив bytearray.
+corrupted_packet = bytearray(packet)
+
+header_size = struct.calcsize(HEADER_FORMAT)
+
+# В строке "ПРИВЕТ SDR":
+#
+# "ПРИВЕТ" занимает 12 байтов UTF-8,
+# пробел занимает 1 байт,
+# буква S находится по индексу 13 внутри PAYLOAD.
+payload_byte_index = 13
+
+# Полный индекс внутри пакета:
+packet_byte_index = header_size + payload_byte_index
+
+original_byte = corrupted_packet[packet_byte_index]
+
+# XOR с 0x01 изменяет младший бит:
+#
+# 0x53 = 01010011 = S
+# 0x52 = 01010010 = R
+corrupted_packet[packet_byte_index] ^= 0x01
+
+corrupted_byte = corrupted_packet[packet_byte_index]
+
+
+print("\nИзменяемый байт внутри пакета:")
+
+print(
+    f"До повреждения:    "
+    f"{original_byte:3d} "
+    f"= 0x{original_byte:02X} "
+    f"= {original_byte:08b}"
+)
+
+print(
+    f"После повреждения: "
+    f"{corrupted_byte:3d} "
+    f"= 0x{corrupted_byte:02X} "
+    f"= {corrupted_byte:08b}"
+)
+
+print("\nПовреждённый пакет:")
+print(bytes(corrupted_packet).hex(" "))
+
+
+# ============================================================
+# Разбор повреждённого пакета
+# ============================================================
+
+received_header = corrupted_packet[:header_size]
+received_payload = corrupted_packet[header_size:]
+
+(
+    received_sync,
+    received_version,
+    received_type,
+    received_sequence,
+    received_length,
+) = struct.unpack(HEADER_FORMAT, received_header)
+
+
+# ============================================================
+# Проверки структуры
+# ============================================================
+
+assert received_sync == SYNC_WORD
+assert received_version == PROTOCOL_VERSION
+assert received_type == MESSAGE_TYPE_TEXT
+assert received_sequence == sequence_number
+assert received_length == len(received_payload)
+
+print("\nВсе проверки заголовка пройдены.")
+
+restored_message = bytes(received_payload).decode("utf-8")
+
+
+print("\nСообщение после повреждения:")
+print(restored_message)
+
+print("\nИсходное сообщение:")
+print(message)
+
+
+# ============================================================
+# Проверка результата эксперимента
+# ============================================================
+
+assert restored_message != message
+
+print("\nПовреждение данных произошло.")
+print("Но заголовок и длина пакета остались правильными.")
+print("Без CRC приёмник не смог определить ошибку.")