fix: support HugeVertex4Insert on offheap serialize

[coderzc]

fix bug #1614

[codecov]

Codecov Report

Merging #1630 (8e7aa74) into master (43b8ae7) will decrease coverage by 0.01%.
The diff coverage is 0.00%.

@@             Coverage Diff              @@
##             master    #1630      +/-   ##
============================================
- Coverage     63.20%   63.19%   -0.02%     
- Complexity     6756     6758       +2     
============================================
  Files           421      421              
  Lines         34642    34642              
  Branches       4797     4797              
============================================
- Hits          21897    21893       -4     
- Misses        10475    10480       +5     
+ Partials       2270     2269       -1     

Impacted Files	Coverage Δ
...om/baidu/hugegraph/backend/cache/OffheapCache.java	57.83% <0.00%> (ø)
...du/hugegraph/backend/tx/GraphIndexTransaction.java	83.58% <0.00%> (-0.53%)	⬇️
...c/main/java/com/baidu/hugegraph/task/HugeTask.java	72.30% <0.00%> (+0.30%)	⬆️

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