Unify time field type of EventMessage struct to i64

[syncpark]

Close #124

• Modify time field type to i64 in EventMessage struct.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.27%. Comparing base (2598d5b) to head (319c20c).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #125      +/-   ##
==========================================
+ Coverage   86.99%   87.27%   +0.28%     
==========================================
  Files          11       11              
  Lines        2330     2350      +20     
==========================================
+ Hits         2027     2051      +24     
+ Misses        303      299       -4     

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