fix: use local TimestampUtil in PgStatement and PgResultset for thread safety

[marcmuel]

TimestampUtil is not thread safe. It raises exeptions when multiple
Threads use ResultSets of one
connection. If PgStatement and PgResultSet use their own TimestampUtil
no synchronize is needed.

Issue: fix: synchronize modification of shared calendar (#921)

[davecramer]

@marcmuel can you fix up the null check issues please ?

[davecramer]

I can commit if you check the box which allows maintainers to commit to this PR

[davecramer]

timestampUtils = new TimestampUtils(! connection.getQueryExecutor().getIntegerDateTimes(), (Provider<TimeZone>) new QueryExecutorTimeZoneProvider(connection.getQueryExecutor()));
and
timestampUtils = new TimestampUtils(! connection.getQueryExecutor().getIntegerDateTimes(), (Provider< TimeZone>)new QueryExecutorTimeZoneProvider(connection.getQueryExecutor()));

fixes this.

[marcmuel]

OK. I added your changes. Thanks.

[marcmuel]

"Allow edits by maintainers" is alredy checked.

[davecramer]

couple small fixes in style and we are good to to...

[marcmuel]

ok. I did it.

[vlsi]

@marcmuel , @tordmjohnson, I am afraid this change does not really solve #921

A single TimestampUtil instance per-ResultSet is still not enough to make it safe concurrent operations on a single ResultSet instance from multiple threads.