Fix PostgreSQL-Compatible Timestamp Handling in SQL Engine

[ljluestc]

This PR resolves Issue #1149 by fixing the inability to insert or update TIMESTAMP values in immudb using PostgreSQL-compatible SQL syntax, which caused errors like org.postgresql.util.PSQLException: ERROR: value is not a timestamp. The issue stemmed from immudb’s SQL engine not handling PostgreSQL timestamp formats (e.g., YYYY-MM-DD HH:MM:SS) or implicit casts, unlike PostgreSQL. The fix enhances the SQL engine and JDBC driver integration to support PostgreSQL-compatible timestamp formats, CURRENT_TIMESTAMP, and epoch milliseconds.

Key changes:

• Updated pkg/database/sql.go to parse PostgreSQL timestamp formats (YYYY-MM-DD HH:MM:SS, ISO 8601, epoch milliseconds) in ParseSQLValue.
• Added support for CURRENT_TIMESTAMP and NOW() in SQL statements.
• Modified pkg/client/jdbc/immudb_driver.go to handle time.Time parameters in JDBC, converting to YYYY-MM-DD HH:MM:SS.
• Added tests in pkg/database/sql_test.go and pkg/client/jdbc/immudb4j_test.go to verify timestamp insertion and querying.
• Addressed write: broken pipe errors by ensuring robust parameter handling.

What are the main choices made to get to this solution?

• Timestamp Parsing: Implemented multiple format parsing (YYYY-MM-DD HH:MM:SS, ISO 8601, epoch) to align with PostgreSQL’s flexibility [].
• JDBC Integration: Converted time.Time to string format in the JDBC driver to ensure compatibility with immudb’s SQL engine [].
• CURRENT_TIMESTAMP Support: Replaced CURRENT_TIMESTAMP and NOW() with formatted timestamps to simplify SQL processing.
• Error Handling: Added detailed error messages for invalid timestamps to improve debugging [].
• Minimal Changes: Focused on SQL engine and JDBC driver, avoiding changes to core storage to maintain stability.