Make get_prepared_metadata() public

[lvboudre]

I would like to pre serialized my rows and reuse the serialization result.
In order to do that I need to:

let my_row = (....)

let prepared_stmt = ...
let ctx = RowSerializationContext::from_prepared(ps.get_prepared_metadata()); /// ERROR: ge_prepared_metadata() is pub(crate) not pub.
let SerializedValues::from_serializable(ctx, my_row)

By making get_prepared_metadata this would make the API more coherent since
SerializedValues, RowSerializationContext are public so is their contructors metadata that ultimately rely on PreparedMetadata which is also public.

[Lorak-mmk]

We plan to address this use case by introducing BoundStatement: #941

SerializedValues is only present in the public API in some ClusterData method - we plan to change this so that users don't have to know about this type at all.

[lvboudre]

@Lorak-mmk

Would it be possible to make this function public in the next minor release?
I've read about #941 but the the PR is for release 1.x.x which is only 15% done and will probably exceed the release date of Feb 15th 2025.