[codex] Support timezone-qualified RowBinary datetimes

[ruslandoga]

Summary

• Preserve timezone-qualified DateTime and DateTime64 RowBinary encoding types instead of rejecting non-UTC annotations.
• Interpret NaiveDateTime values in the ClickHouse type timezone while continuing to encode DateTime values by instant.
• Update RowBinary regression coverage and timezone documentation for the new behavior.

Fixes #353.

Checks

• mix test