Add tool for code coverage

[testn]

Due to the mistake I made earlier, I just noticed that the code coverage we had wasn't good enough. Let's add the tool to cover it? I plan to use c8 to do this. @sidorares, if you are ok, we can probably figure out to add the output of this to github action as well?

-----------------------------------|---------|----------|---------|---------|-----------------------
File                               | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s
-----------------------------------|---------|----------|---------|---------|-----------------------
All files                          |   88.27 |    83.84 |   78.96 |   88.27 |
 node-mysql2                       |   70.56 |    83.72 |   64.44 |   70.56 |
  index.js                         |   96.29 |      100 |   66.66 |   96.29 | 68,76,80
  promise.js                       |   66.78 |    81.81 |    64.1 |   66.78 | ...88-504,520,529-540
 node-mysql2/lib                   |   79.02 |    81.66 |   82.25 |   79.02 |
  auth_41.js                       |     100 |      100 |     100 |     100 |
  connection.js                    |   74.14 |    84.88 |   77.77 |   74.14 | ...58,762-763,895-934
  connection_config.js             |   90.23 |    82.53 |     100 |   90.23 | ...19,229-230,244-250
  helpers.js                       |   80.95 |      100 |      50 |   80.95 | 31-36,43-48
  packet_parser.js                 |   77.43 |    88.46 |      75 |   77.43 | ...4-61,84-97,148-161
  pool.js                          |   86.79 |    78.68 |     100 |   86.79 | ...55,169-170,176-178
  pool_cluster.js                  |    68.9 |    62.96 |   80.95 |    68.9 | ...50,254-255,261-270
  pool_config.js                   |   91.66 |    57.14 |     100 |   91.66 | 8-9
  pool_connection.js               |   73.84 |    88.88 |   66.66 |   73.84 | 14,29-31,34-44,53-54
  server.js                        |     100 |      100 |     100 |     100 |
 node-mysql2/lib/auth_plugins      |   64.61 |       70 |    87.5 |   64.61 |
  caching_sha2_password.js         |   81.55 |     61.9 |     100 |   81.55 | ...90-91,94-96,98-101
  mysql_native_password.js         |   84.37 |    85.71 |     100 |   84.37 | 18-22
  sha256_password.js               |      25 |      100 |      50 |      25 | 13-19,22-59
 node-mysql2/lib/commands          |   79.76 |    84.82 |   72.15 |   79.76 |
  auth_switch.js                   |   87.73 |    81.81 |     100 |   87.73 | ...-63,82-83,90-93,99
  binlog_dump.js                   |   37.61 |      100 |       0 |   37.61 | ...70-76,81-93,98-101
  change_user.js                   |     100 |      100 |     100 |     100 |
  client_handshake.js              |    61.5 |    76.66 |    62.5 |    61.5 | ...40,164,178,189-192
  close_statement.js               |     100 |      100 |     100 |     100 |
  command.js                       |   85.45 |      100 |   66.66 |   85.45 | 14-21
  execute.js                       |   96.26 |    83.33 |     100 |   96.26 | 56-57,86-87
  index.js                         |     100 |      100 |     100 |     100 |
  ping.js                          |      50 |      100 |       0 |      50 | 12-14,17-25,28-33
  prepare.js                       |   94.61 |     90.9 |     100 |   94.61 | 24-26,98-99,109-110
  query.js                         |   90.65 |    90.66 |    82.6 |   90.65 | ...73-274,278,314-315
  quit.js                          |     100 |      100 |     100 |     100 |
  register_slave.js                |   51.85 |      100 |       0 |   51.85 | 8-11,14-17,20-24
  server_handshake.js              |    75.3 |    54.16 |     100 |    75.3 | ...23,125,128,130-132
 node-mysql2/lib/constants         |     100 |      100 |     100 |     100 |
  charset_encodings.js             |     100 |      100 |     100 |     100 |
  charsets.js                      |     100 |      100 |     100 |     100 |
  client.js                        |     100 |      100 |     100 |     100 |
  commands.js                      |     100 |      100 |     100 |     100 |
  cursor.js                        |     100 |      100 |     100 |     100 |
  encoding_charset.js              |     100 |      100 |     100 |     100 |
  errors.js                        |     100 |      100 |     100 |     100 |
  field_flags.js                   |     100 |      100 |     100 |     100 |
  server_status.js                 |     100 |      100 |     100 |     100 |
  session_track.js                 |     100 |      100 |     100 |     100 |
  ssl_profiles.js                  |     100 |      100 |     100 |     100 |
  types.js                         |     100 |      100 |     100 |     100 |
 node-mysql2/lib/packets           |   86.88 |    83.63 |   83.82 |   86.88 |
  auth_switch_request.js           |     100 |      100 |     100 |     100 |
  auth_switch_request_more_data.js |   93.93 |      100 |      75 |   93.93 | 29-30
  auth_switch_response.js          |     100 |      100 |     100 |     100 |
  binary_row.js                    |   70.83 |      100 |       0 |   70.83 | 10-11,14-15,19-28
  binlog_dump.js                   |   51.51 |      100 |       0 |   51.51 | 13-17,20-30
  change_user.js                   |   73.19 |       50 |     100 |   73.19 | ...,62-80,86-87,89-90
  close_statement.js               |     100 |      100 |     100 |     100 |
  column_definition.js             |   97.18 |      100 |   85.71 |   97.18 | 106-109
  execute.js                       |      98 |    93.33 |     100 |      98 | 31,55-56
  handshake.js                     |   91.96 |    76.92 |     100 |   91.96 | 24-26,84-85,92-95
  handshake_response.js            |   89.65 |    77.27 |     100 |   89.65 | ...3-94,96-97,119-123
  index.js                         |   93.83 |    77.77 |      80 |   93.83 | 53-61
  packet.js                        |   86.83 |    83.11 |   88.88 |   86.83 | ...73,876-886,895-898
  prepare_statement.js             |     100 |      100 |     100 |     100 |
  prepared_statement_header.js     |     100 |      100 |     100 |     100 |
  query.js                         |     100 |      100 |     100 |     100 |
  register_slave.js                |    32.6 |      100 |       0 |    32.6 | 11-18,21-43
  resultset_header.js              |   91.81 |    87.09 |     100 |   91.81 | ...2-74,97-98,104-105
  ssl_request.js                   |      48 |      100 |       0 |      48 | 8-10,13-22
  text_row.js                      |    61.7 |    57.14 |   33.33 |    61.7 | ...,24-26,34-36,38-40
 node-mysql2/lib/parsers           |   95.56 |     90.6 |   83.33 |   95.56 |
  binary_parser.js                 |   95.69 |    89.06 |     100 |   95.69 | 36,50-51,174-178
  parser_cache.js                  |   88.67 |       90 |      50 |   88.67 | 41-43,45-47
  string.js                        |     100 |    84.61 |     100 |     100 | 28
  text_parser.js                   |    96.6 |    93.54 |     100 |    96.6 | 78-79,194-198
-----------------------------------|---------|----------|---------|---------|-----------------------