Allow `Bind` impl to differ from `Serialize` impl (for DateTime64)

[Smona]

Use case

AFAICT, ClickHouse when using the row binary format requires integer timestamps with matching precision for DateTime64 fields. However, when using DateTime64 values in queries the that format is not supported. not only that, but there's no way to diretly use those millisecond timestamps in toDateTime64 that I can find. So currently, binding chrono DateTimes to queries requires custom formatting code.

Ideally it would be possible to create a DateTime64(chrono::DateTime<Utc>) newtype that can be both used in Row structs without a serde_with attribute, and passed directly into query.bind() while working as expected, but since the Bind trait is sealed and already implemented for all Serialize types this isn't possible.

Describe the solution you'd like

Either provide an in-house DateTime64 type, or allow users to implement their own types that have disjoint Bind and Serialize implementations.

Describe the alternatives you've considered

Implement a simple helper function to format DateTime<Utc values in a query-compatible format. The problem with this is there is no way to avoid query errors at compile time from directly passing in DateTime<Utc, since bind() will happily accept any value that implements Serialize.

[slvrtrn]

Either provide an in-house DateTime64 type, or allow users to implement their own types that have disjoint Bind and Serialize implementations.

We are going to provide our own types at certain point, see #236

[Smona]

Nice! That's the cleanest solution I can come up with, although it doesn't touch on the extensibility benefit of unsealing the Bind trait to allow user-created field implementations, so I figured this request was a little different.

That said, feel free to close this issue if you don't think the extensibility piece is valuable; it might not be if all supported CH fields are well covered. And let me know if help is wanted on #236! We are very interested in improving type safety around row serde and query binding :)