feat: Improve support for Timestamp DT

[ovr]

Hello!

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[coveralls]

Pull Request Test Coverage Report for Build 4479158152

• 30 of 42 (71.43%) changed or added relevant lines in 5 files are covered.
• 53 unchanged lines in 7 files lost coverage.
• Overall coverage decreased (-6.9%) to 82.306%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/tokenizer.rs	0	1	0.0%
src/parser.rs	9	14	64.29%
src/ast/data_type.rs	7	13	53.85%

Files with Coverage Reduction	New Missed Lines	%
src/ast/data_type.rs	1	68.09%
src/ast/mod.rs	2	70.48%
src/ast/query.rs	2	85.07%
tests/sqlparser_snowflake.rs	2	96.43%
src/parser.rs	4	84.25%
tests/sqlparser_postgres.rs	8	97.06%
tests/sqlparser_common.rs	34	97.19%

Totals
Change from base Build 1513769481:	-6.9%
Covered Lines:	5610
Relevant Lines:	6816

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💛 - Coveralls