Fix dropped change flags + FIDI parsing

- capture.py: DirectSniffer/GsmtapListener yield (type, data, flags),
  CaptureManager passes flags to insert_message (change flags were
  previously dropped, leaving every change row with flags=0)
- protocol.py: add _parse_fidi (1-byte value) — FIDI was mis-mapped to
  _parse_change (4-byte flags), so FIDI messages were silently dropped
- database.py: pass flags into decode_sniff_msg
- decode.py: decode_change(flags) reads flags directly; decode_sniff_msg
  gains flags parameter; change messages no longer require non-empty data
- tests: fix FIDI test, add change/fidi decode tests (43 total)

tests/test_protocol.py

@@ -83,13 +83,14 @@ class TestParseMessage(unittest.TestCase):
         self.assertEqual(msg.flags, CHANGE_FLAG_TIMEOUT_WT)
 
     def test_fidi_message(self):
-        payload = struct.pack('<I', 0x97)  # Fi=9, Di=7
+        payload = b'\x97'  # Fi=9, Di=7
         buf = _build_hdr(SIMTRACE_MSGC_SNIFF, SIMTRACE_MSGT_SNIFF_FIDI,
                          payload=payload)
         msg, consumed = parse_message(buf)
         self.assertEqual(msg.type, 'fidi')
-        self.assertEqual(len(msg.data), 0)
-        self.assertEqual(msg.flags, 0x97)
+        self.assertEqual(len(msg.data), 1)
+        self.assertEqual(msg.data, b'\x97')
+        self.assertEqual(msg.flags, 0)
 
     def test_atr_message(self):
         atr = b'\x3b\x9e\x12\x34\x56\x78\x90'