COPY: handle DateTime kind mismatch with a clearer error (or normalize)

[WailedParsley36]

Binary COPY is strict about types and does no implicit cast, so writing a Kind=Utc DateTime to a timestamp without time zone column throws a low-level Npgsql converter error. The parameterized insert path hides this via driver inference + implicit cast.

Options to consider:

• Detect the mismatch and throw a clear, actionable message naming the column.
• Optionally normalize the DateTime.Kind to match the column's timestamp type.

At minimum this is documented on the Bulk COPY page; a friendlier runtime experience would help.