[ISSUE #251]Support avg function in WindowStream

[Jargon9]

Hi teams, I have completed the main part of avg calculation. Could you please review the code?

• Besides, I'm a little confused. For the average calculation in the Accumulator, is the merge only allowed for the same type accumulator?
• I wrote an example to test. Here is the test result.

time:23:00:58.644, input:6
time:23:00:59.883, input:7
time:23:01:01.492, input:8
[2023-01-27 23:00:55 - 2023-01-27 23:01:00](key=key, value=6.0)
time:23:01:13.550, input:9
[2023-01-27 23:01:00 - 2023-01-27 23:01:05](key=key, value=8.0) ```

[ni-ze]

Good catch, Thanks very much your pr.

1. merge is a reserved method, It use to merge two AvgAccumulator during calculation process；
2. the result of example seems not very accurate，pr 263 maybe solve this problem, please check this example again after that pr merged；
3. It is best to stop the RocketMQStream when program exit，like other examples.

[ni-ze]

@Jargon9 你好，能否看看这个pr，最近可能发版本，能带上最好。

[Jargon9]

@Jargon9 你好，能否看看这个pr，最近可能发版本，能带上最好。

@ni-ze 好的！十分感谢帮忙cr代码。不好意思我前几天有点忙，周末会继续完成它的。

[Jargon9]

Hi teams, I found that the log truncation of the previous results is incomplete. I retested the function. It should be OK.
Besides, thank you for your help, I add a WindowAvg-shutdown-hood when program exit , like other examples.

time:21:54:12.507, input:1
time:21:54:17.498, input:2
[2023-02-05 21:54:00 - 2023-02-05 21:54:15](key=key, value=1.0)
time:21:54:22.507, input:3
time:21:54:27.516, input:4
time:21:54:32.531, input:5
[2023-02-05 21:54:15 - 2023-02-05 21:54:30](key=key, value=3.0)
time:21:54:37.538, input:6
time:21:54:42.545, input:7
time:21:54:47.560, input:8
[2023-02-05 21:54:30 - 2023-02-05 21:54:45](key=key, value=6.0)
time:21:54:52.571, input:9
time:21:55:44.630, input:1
[2023-02-05 21:54:45 - 2023-02-05 21:55:00](key=key, value=8.5)
time:21:55:48.642, input:2
[2023-02-05 21:55:30 - 2023-02-05 21:55:45](key=key, value=1.0)
time:21:55:52.651, input:3
time:21:55:56.657, input:4
time:21:56:00.669, input:5
[2023-02-05 21:55:45 - 2023-02-05 21:56:00](key=key, value=3.0)
time:21:56:04.677, input:6
time:21:56:08.681, input:7
time:21:56:12.691, input:8
time:21:56:16.701, input:9
[2023-02-05 21:56:00 - 2023-02-05 21:56:15](key=key, value=6.5)

[codecov-commenter]

Codecov Report

Merging #259 (e6eec5d) into develop (608ccae) will not change coverage.
The diff coverage is 0.00%.

@@           Coverage Diff           @@
##           develop    #259   +/-   ##
=======================================
  Coverage     0.00%   0.00%           
=======================================
  Files           85      87    +2     
  Lines         3027    3084   +57     
  Branches       296     301    +5     
=======================================
- Misses        3027    3084   +57     

Impacted Files	Coverage Δ
...eams/core/function/accumulator/AvgAccumulator.java	0.00% <0.00%> (ø)
...ocketmq/streams/core/rstream/WindowStreamImpl.java	0.00% <0.00%> (ø)
.../rocketmq/streams/core/util/OperatorNameMaker.java	0.00% <ø> (ø)
...he/rocketmq/streams/examples/window/WindowAvg.java	0.00% <0.00%> (ø)

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