optimize kout/kneighbor count (avoid copying set)

[javeme]

Change-Id: I6181aee91ad9585744c53b7207d76205817e7529

[codecov]

Codecov Report

Merging #1550 (97b6001) into master (5df904b) will decrease coverage by 0.06%.
The diff coverage is 0.00%.

@@             Coverage Diff              @@
##             master    #1550      +/-   ##
============================================
- Coverage     60.34%   60.28%   -0.07%     
+ Complexity     6393     6391       -2     
============================================
  Files           417      417              
  Lines         34289    34298       +9     
  Branches       4735     4738       +3     
============================================
- Hits          20693    20677      -16     
- Misses        11460    11487      +27     
+ Partials       2136     2134       -2     

Impacted Files	Coverage Δ
...m/baidu/hugegraph/api/traversers/KneighborAPI.java	0.00% <0.00%> (ø)
...va/com/baidu/hugegraph/api/traversers/KoutAPI.java	0.00% <0.00%> (ø)
...com/baidu/hugegraph/serializer/JsonSerializer.java	50.00% <0.00%> (+0.46%)	⬆️
...ava/com/baidu/hugegraph/serializer/Serializer.java	0.00% <ø> (ø)
.../traversal/algorithm/records/KneighborRecords.java	0.00% <0.00%> (ø)
...graph/traversal/algorithm/records/KoutRecords.java	0.00% <0.00%> (ø)
...va/com/baidu/hugegraph/auth/HugeAuthenticator.java	34.78% <0.00%> (-5.44%)	⬇️
...ain/java/com/baidu/hugegraph/task/TaskManager.java	69.06% <0.00%> (-1.44%)	⬇️
...in/java/com/baidu/hugegraph/auth/HugeResource.java	77.92% <0.00%> (-1.30%)	⬇️
.../java/com/baidu/hugegraph/auth/RolePermission.java	90.58% <0.00%> (-1.18%)	⬇️
... and 5 more

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