fix: correct SqlMetaData constructor selection for datetime2/datetimeoffset/time TVP columns

The previous fix for #393 used `match name, dbType with` where `name`
is the column name (e.g. "CreatedAt"), not the SQL type name. This meant
the pattern | "datetime2", SqlDbType.DateTime2 -> ... would never fire
unless the column happened to be literally named "datetime2".

The correct fix is to match on `dbType` alone, which always contains the
actual SQL type. This ensures that all DateTime2, DateTimeOffset and Time
TVP columns use SqlMetaData(name, dbType, 0uy, scale) rather than
SqlMetaData(name, dbType, precision, scale), avoiding the ArgumentException
"Metadata for field 'X' did not match the original record's metadata"
when the precision byte doesn't equal what SQL Server expects.

Closes #393

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: 2 people

src/SqlClient.DesignTime/DesignTime.fs

@@ -542,11 +542,15 @@ type DesignTime private() =
                         let precision = byte p.Precision
                         let scale = byte p.Scale
                         if typeInfo.IsFixedLength then
-                            match name, dbType with
-                            | "datetime2"     , SqlDbType.DateTime2
-                            | "datetimeoffset", SqlDbType.DateTimeOffset
-                            | "time"          , SqlDbType.Time ->
+                            match dbType with
+                            | SqlDbType.DateTime2
+                            | SqlDbType.DateTimeOffset
+                            | SqlDbType.Time ->
                                 // https://github.com/fsprojects/FSharp.Data.SqlClient/issues/393
+                                // These types use (name, dbType, precision, scale) but precision must be 0,
+                                // not the value from sys.columns (which is 10 for datetimeoffset etc.).
+                                // The previous match on `name` was incorrect — it compared the column name
+                                // (e.g. "CreatedAt") to the type name, so the fix never fired.
                                 <@@ SqlMetaData(name, dbType, 0uy, scale) @@>
                             | _ ->
                                 // https://github.com/fsprojects/FSharp.Data.SqlClient/issues/345