Port or enable DateTimeUtilsSuite timestamp format tests in Comet

[parthchandra]

While working on #3730, it was discovered that we are not testing various date time formats because the tests in Spark's DateTimeUtilsSuite are never being called.
The test suite is in sql/catalyst and does not extend either SQLTestUtils or CometTestBase. The tests in this subproject are not part of Comet CI.
Also, IgnoreComet is not available in this subproject and it may not be possible to disable the tests selectively.

The following tests are relevant -

Test	Format coverage
string to timestamp	YYYY-MM-DD, YYYY-MM-DDTHH:mm:ss, space-vs-T separator, time-only (HH:mm:ss, T18:12:15), timezone suffixes (Z, UTC, GMT±hh:mm, ±hhmm, ±h:m, named tz like Europe/Moscow), milliseconds/microseconds, nanosecond truncation, whitespace/control char
permutations, ~20 invalid formats that must return None
SPARK-35780: support full range of timestamp string	Negative years (-1969-…), 5-digit years (99999-…), zero-padded years, Long.MaxValue/Long.MinValue boundary timestamps, integer overflow in individual fields
SPARK-37326: stringToTimestampWithoutTimeZone with allowTimeZone	TIMESTAMP_NTZ with allowTimeZone=true/false and a +hh:mm suffix
SPARK-15379: special invalid date string	Feb 29 on non-leap year, Apr 31 — must be rejected by both toDate and stringToTimestamp
trailing characters while converting string to timestamp	Trailing garbage after a valid ISO timestamp (e.g. 2019-10-31T10:59:23Z:::) must return None
SPARK-29012: special timestamp values	Keyword strings: Epoch, NOW, Yesterday, Today, tomorrow (with optional trailing timezone)
SPARK-35979: special timestamp without time zone values	Same keyword strings for TIMESTAMP_NTZ via convertSpecialTimestampNTZ

It might be easier to copy the format-related tests from DateTimeUtilsSuite into a new or existing Comet test class (e.g. CometDateTimeUtilsSuite), as opposed to trying to enable catalyst tests in Comet CI.