does this seem correct if my type is just `struct DateTime(OffsetDateTime);`:
```rust
impl Schema for DateTime {
    const SCHEMA: &'static NamedType = &NamedType {
        name: "DateTime",
        ty: &SdmTy::NewtypeStruct(&NamedType {
            name: "OffsetDateTime",
            ty: &SdmTy::Tuple(&[
                // year
                i32::SCHEMA,
                // ordinal
                u16::SCHEMA,
                // hour
                u8::SCHEMA,
                // minute
                u8::SCHEMA,
                // second
                u8::SCHEMA,
                // nanosecond
                u32::SCHEMA,
                // offset hours
                i8::SCHEMA,
                // offset minutes
                i8::SCHEMA,
                // offset seconds
                i8::SCHEMA,
            ]),
        }),
    };
}
```
?