Optimize query execution in easy count(*) cases

[JackieTien97]

If all seq data, and compaction is well done, we will only need to get one TimeSeriesMetadata to calcuate count for each device. However, according to the profiler result, we found a lot of overhead in SeriesScanUtil, in this pr we will try to save the useless code execution.

1. needless set in initQueryDatasource in some cases
2. save device.toString() if cache hit in TimeSeriesMetadataCache
3. use result of map.get() to judge whether a key exists instead of using map,containsKey before calling map.get

[codecov]

Codecov Report

Attention: Patch coverage is 73.17073% with 11 lines in your changes missing coverage. Please review.

Project coverage is 39.35%. Comparing base (07e0d21) to head (a157ac0).
Report is 8 commits behind head on master.

Files with missing lines	Patch %	Lines
...ne/execution/fragment/FragmentInstanceContext.java	62.50%	6 Missing ⚠️
...torageengine/dataregion/tsfile/TsFileResource.java	75.00%	4 Missing ⚠️
.../storageengine/buffer/TimeSeriesMetadataCache.java	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##             master   #15111   +/-   ##
=========================================
  Coverage     39.35%   39.35%           
  Complexity      193      193           
=========================================
  Files          4596     4596           
  Lines        295732   295806   +74     
  Branches      36856    36876   +20     
=========================================
+ Hits         116386   116424   +38     
- Misses       179346   179382   +36     

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[sonarqubecloud]

Quality Gate passed

Issues
3 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud