This PR adds support for the TIMESTAMPDIFF() function

Key changes include:

• Implemented the sqlTimestampdiff function to calculate the difference between two timestamps, handling various units such as SECOND, MINUTE, HOUR, DAY, WEEK, MONTH, QUARTER, and YEAR.
• Added a new test case (testTimestampDiff) to ensure the function works as expected for different units and date combinations, including both positive and negative results.