Logging improvements

[fiffu]

• [x] Refactoring to improve traceability
  • Get rid of various logging endpts exposed by engine
  • Move logging params to ctx
  • Consolidate to top-level module funcs Infof(ctx, msg, ...args), Errorf(ctx, err, msg, ...args) and so on
• [x] Support request tracing
  • Ensure log messages are prefixed by traceID