Optimize for statistic data structures

[sczyh30]

Describe what this PR does / why we need it

Bug fix and optimization for statistic data structures, and update test cases.

Describe how you did it

• Fix a bug: old position is not cleaned when inserting into a new (empty) position
• Reuse buckets for optimization
• The strategy is now changed: deprecated buckets will not be reset until newer time triggered. LeapArray is responsible for filtering the deprecated buckets (e.g. in list or values)
• Update test cases

Describe how to verify it

See updated test cases.

[CarpenterLee]

LGTM

[codecov-io]

Codecov Report

Merging #47 into master will increase coverage by 0.25%.
The diff coverage is 81.25%.

@@             Coverage Diff              @@
##             master      #47      +/-   ##
============================================
+ Coverage     45.73%   45.98%   +0.25%     
- Complexity      550      557       +7     
============================================
  Files           113      113              
  Lines          3800     3801       +1     
  Branches        533      529       -4     
============================================
+ Hits           1738     1748      +10     
+ Misses         1849     1841       -8     
+ Partials        213      212       -1

Impacted Files	Coverage Δ	Complexity Δ
...baba/csp/sentinel/slots/statistic/base/Window.java	97.29% <100%> (+20.82%)	14 <0> (+2)	⬆️
...ntinel/slots/statistic/metric/WindowLeapArray.java	80% <100%> (+9.03%)	6 <1> (-1)	⬇️
.../csp/sentinel/slots/statistic/base/WindowWrap.java	76.92% <66.66%> (-3.08%)	5 <1> (+1)
...a/csp/sentinel/slots/statistic/base/LeapArray.java	76.92% <66.66%> (-2.03%)	15 <2> (+4)
...ibaba/csp/sentinel/eagleeye/EagleEyeLogDaemon.java	24.24% <0%> (-6.07%)	5% <0%> (-1%)
...a/com/alibaba/csp/sentinel/node/StatisticNode.java	64.91% <0%> (+3.5%)	16% <0%> (+1%)	⬆️
...a/csp/sentinel/slots/statistic/base/LongAdder.java	19.14% <0%> (+4.25%)	5% <0%> (+1%)	⬆️

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