MMSIs should be output as strings, with zero prefixes preserved

[tkurki]

Works with canboat with "002442103" as MMSI

echo '2019-01-25T19:00:00.326Z,7,129793,43,255,26,04,77,43,25,00,bd,73,b1,02,ae,39,ef,1e,03,f0,db,c4,28,c9,c2,00,01,46,10,00,fc' | ./rel/darwin-arm64/analyzer -json | tail -1 | json
INFO 2026-01-29T20:07:21.093Z [analyzer] Detected FAST format with all frames on one line
{
  "timestamp": "2019-01-25T19:00:00.326Z",
  "prio": 7,
  "src": 43,
  "dst": 255,
  "pgn": 129793,
  "description": "AIS UTC and Date Report",
  "fields": {
    "Message ID": "Base station report",
    "Repeat Indicator": "Initial",
    "User ID": "002442103",
    "Longitude": 4.5183933,
    "Latitude": 51.899435,
    "Position Accuracy": "High",
    "RAIM": "in use",
    "Reserved": "00",
    "Position Time": "18:59:59.0000",
    "Communication State": "C9 C2 00",
    "AIS Transceiver information": "Channel A VDL reception",
    "Position Date": "2019.01.25",
    "GNSS type": "GPS"
  }
}

but canboatjs mangles the MMSI as a number

echo '2019-01-25T19:00:00.326Z,7,129793,43,255,26,04,77,43,25,00,bd,73,b1,02,ae,39,ef,1e,03,f0,db,c4,28,c9,c2,00,01,46,10,00,fc' | dist/bin/analyzerjs.js | json
{
  "pgn": 129793,
  "prio": 7,
  "src": 43,
  "dst": 255,
  "timestamp": "2019-01-25T19:00:00.326Z",
  "input": [
    "2019-01-25T19:00:00.326Z,7,129793,43,255,26,04,77,43,25,00,bd,73,b1,02,ae,39,ef,1e,03,f0,db,c4,28,c9,c2,00,01,46,10,00,fc"
  ],
  "description": "AIS UTC and Date Report",
  "fields": {
    "Message ID": "Base station report",
    "Repeat Indicator": "Initial",
    "User ID": 2442103,
    "Longitude": 4.5183933,
    "Latitude": 51.899435,
    "Position Accuracy": "High",
    "RAIM": "in use",
    "Reserved1": 0,
    "Position Time": "18:59:59",
    "Communication State": 49865,
    "AIS Transceiver information": "Channel A VDL reception",
    "Position Date": "2019.01.25",
    "Reserved2": 0,
    "GNSS type": "GPS"
  },
  "id": "aisUtcAndDateReport"
}

canboat/canboat#267