[#140] Support nested async trace

[feelform]

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[feelform]

LCOV of commit c92b2db during CI #333

Summary coverage rate:
  lines......: 82.2% (2576 of 3135 lines)
  functions..: 77.7% (518 of 667 functions)
  branches...: 68.9% (999 of 1450 branches)

Files changed coverage rate:
                                                                               |Lines       |Functions  |Branches    
  Filename                                                                     |Rate     Num|Rate    Num|Rate     Num
  ===================================================================================================================
  lib/agent.js                                                                 |83.3%     54|75.0%    12|71.4%     14
  lib/context/context-manager.js                                               |42.9%     21| 0.0%     6| 0.0%      8
  lib/instrumentation/context/local-storage.js                                 |90.9%     11| 100%     5|50.0%      2
  lib/instrumentation/instrument-method-context.js                             |83.3%      6|75.0%     4|    -      0
  lib/instrumentation/instrument-method.js                                     |93.1%     72| 100%     6|82.1%     56
  lib/instrumentation/module/express.js                                        |86.7%     15| 100%     1| 100%      2
  lib/instrumentation/module/express/express-route-interceptor.js              |90.0%     10| 100%     2|66.7%      6
  lib/instrumentation/module/express/patch-layer.js                            |90.7%     54| 100%     7|76.3%     38
  lib/instrumentation/module/koa-router.js                                     |80.0%     10| 100%     1|50.0%      2
  lib/instrumentation/module/koa/koa-register-interceptor.js                   |75.0%     40| 100%     3|62.1%     29
  lib/instrumentation/module/mysql.js                                          |88.2%     17| 100%     1|50.0%      2
  lib/instrumentation/module/mysql/mysql-cluster-of-interceptor.js             |90.0%     10| 100%     3|50.0%      2
  lib/instrumentation/module/mysql/mysql-create-connection-interceptor.js      | 100%     16| 100%     3|50.0%      2
  lib/instrumentation/module/mysql/mysql-create-pool-cluster-interceptor.js    |90.0%     10| 100%     3|50.0%      2
  lib/instrumentation/module/mysql/mysql-create-pool-interceptor.js            | 100%     14| 100%     4|50.0%      4
  lib/instrumentation/module/mysql/mysql-get-connection-interceptor.js         |90.5%     21| 100%     4|66.7%     12
  lib/instrumentation/module/mysql2.js                                         |88.2%     17| 100%     1|50.0%      2