feat: add meta file to DB system

[azhsmesos]

The user can clearly see the current file data, and can easily do some operations, such as the user can clear the old data file.

zhaozhenhang@zhaozhenhangdeMacBook-Pro nutsdbtest % ls
0.dat		1.dat		2.dat		3.dat		4.dat		5.dat		6.dat		7.dat		meta.json
zhaozhenhang@zhaozhenhangdeMacBook-Pro nutsdbtest % cat meta.json
{
     "fileName": "0.dat",
     "minTs": 1670947210,
     "maxTs": 1670947213,
     "entryCount": 138,
     "entryBytes": 8202
}
{
     "fileName": "1.dat",
     "minTs": 1670947213,
     "maxTs": 1670947216,
     "entryCount": 134,
     "entryBytes": 8174
}
{
     "fileName": "2.dat",
     "minTs": 1670947216,
     "maxTs": 1670947218,
     "entryCount": 134,
     "entryBytes": 8174
}
{
     "fileName": "3.dat",
     "minTs": 1670947218,
     "maxTs": 1670947220,
     "entryCount": 134,
     "entryBytes": 8174
}
{
     "fileName": "4.dat",
     "minTs": 1670947220,
     "maxTs": 1670947222,
     "entryCount": 134,
     "entryBytes": 8174
}
{
     "fileName": "5.dat",
     "minTs": 1670947222,
     "maxTs": 1670947225,
     "entryCount": 134,
     "entryBytes": 8174
}
{
     "fileName": "6.dat",
     "minTs": 1670947225,
     "maxTs": 1670947227,
     "entryCount": 134,
     "entryBytes": 8174
}

[azhsmesos]

The current operation is only logged when the segment file is full, so it has little impact on performanc.

[elliotchenzichang]

Hi, just wondering how to UnMarshal this file to go object in runtime. Seems that it's not a JSON array schema in this file.