Fix timestamp-to-date conversion

[gvdutra]

Summary

• return a plain java.util.Date when converting timestamp data to Date metadata
• keep timestamp access and JDBC timestamp writes unchanged
• add regression coverage for conversion, null handling, and JDBC writes

Root cause

Date conversion delegated directly to the source metadata. For timestamp fields, that returned the original java.sql.Timestamp, so the field metadata changed to Date while the runtime value did not.

The conversion is now normalized only when the destination type is Date, avoiding changes to timestamp consumers and preserving timestamp precision in existing database paths.

Validation

• ./mvnw -pl core -Dtest=ValueMetaTimestampTest test
• ./mvnw -pl core test
• ./mvnw -pl core -DskipTests spotless:check
• git diff --check

Closes #5651