Fix | ThreadPoolExecutor thread preventing JVM from exiting

[rene-ye]

Changed a thread used to initialize ScheduledThreadPoolExecutor to daemon so the JVM can exit in specific bulkcopy scenarios.

[codecov-io]

Codecov Report

Merging #944 into dev will decrease coverage by 0.01%.
The diff coverage is 100%.

@@             Coverage Diff              @@
##                dev     #944      +/-   ##
============================================
- Coverage     50.55%   50.53%   -0.02%     
+ Complexity     2918     2916       -2     
============================================
  Files           120      120              
  Lines         27984    27987       +3     
  Branches       4678     4678              
============================================
- Hits          14146    14143       -3     
- Misses        11546    11551       +5     
- Partials       2292     2293       +1

Flag	Coverage Δ	Complexity Δ
#JDBC42	50.13% <100%> (+0.02%)	2880 <1> (+2)	⬆️
#JDBC43	50.45% <100%> (-0.06%)	2909 <1> (-6)

Impacted Files	Coverage Δ	Complexity Δ
...java/com/microsoft/sqlserver/jdbc/SharedTimer.java	82.14% <100%> (+2.14%)	10 <1> (ø)	⬇️
...ncurrentlinkedhashmap/ConcurrentLinkedHashMap.java	38.36% <0%> (-1.3%)	42% <0%> (-3%)
...om/microsoft/sqlserver/jdbc/ReaderInputStream.java	43.95% <0%> (-1.1%)	15% <0%> (ø)
...c/main/java/com/microsoft/sqlserver/jdbc/Util.java	61.85% <0%> (-0.44%)	89% <0%> (-1%)
...rc/main/java/com/microsoft/sqlserver/jdbc/dtv.java	68.47% <0%> (-0.12%)	0% <0%> (ø)
...m/microsoft/sqlserver/jdbc/SQLServerResultSet.java	43.56% <0%> (+0.07%)	315% <0%> (ø)	⬇️
...n/java/com/microsoft/sqlserver/jdbc/DataTypes.java	79.92% <0%> (+0.19%)	6% <0%> (+1%)	⬆️
...rc/main/java/com/microsoft/sqlserver/jdbc/DDC.java	47.3% <0%> (+0.43%)	112% <0%> (+1%)	⬆️

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