Serialization refactor: add new serialization traits

[piodul]

Sub-task of #463.

Let's use the convention introduced in the not-yet-done deserialization refactor and let's name the new traits SerializeCql and SerializeRow:

pub trait SerializeRow {
    fn serialize(&self, ctx: &RowSerializationContext<'_>, out: &mut impl std::io::Write) -> Result<(), std::io::Error>;
}

pub trait SerializeCql {
    fn serialize(&self, typ: &CqlType, out: &mut impl std::io::Write) -> Result<(), std::io::Error>;
}

Instead of std::io::Write, perhaps we could use a different trait that abstracts away appending data to a buffer (bytes::BufMut?). Using a trait instead of e.g. &mut Vec<u8> will let us to very easily implement size hints like here: #582 based on the existing serialize() method.

The RowSerializationContext should contain information about the bind markers: column names and their types. Later, we may add more stuff there.

As this change will affect all Session::query and Session::execute calls which should be ubiquitous in the user codebase, we should make it as easy as possible to migrate to the new API, preferably step by step.

Current serialization API is heavily based on SerializedValues type which is an untyped container for serialized values. Session::{execute,query} receive the argument list as an impl ValueList type - which is just a trait that allows to convert the type to SerializedValues. In general, we should implement SerializeRow for each type that implements ValueList, which also includes SerializedValues.

• Calls like session.execute(&prepared, (1, 2, 3)) should work automatically out of the box as we will implement SerializeRow for types that implement SerializedValues, and SerializeCql for types that implement Value. This should be the most common case.
• In a generic context like session.execute(&prepared, generic_list) where generic_list: impl ValueList, the piece of code should be adjusted so that generic_list.serialized()? is called instead - which will convert to SerializedValues which does implement the new SerializedRow.
• For the case of user impls of ValueList and Value, we can provide macros (not necessarily procedural) that generate a SerializedRow/SerializedCql implementation based on the existing ValueList/Value.

It will be necessary to update some examples and documentation, but I don't expect it to be much work compared to the deserialization refactor.

Tasks

Beta Give feedback

1. Serialization refactor: implement SerializeRow and SerializeCql for current implementors of ValueList and Value #821
   +0
   
2. Serialization refactor: adjust the codebase to use SerializeRow and SerializeCql in the public API #822
   +0
   

[piodul]

The issue #802 depends on the SerializeRow and SerializeCql traits introduced by this task. I think just those traits + impls of 2-3 trivial types should be added first, in a separate PR in order to unblock it.

[piodul]

Definitions of the traits have been merged to main (#819). To complete the task, we further need to:

• Implement the new traits for the existing types that support Value and ValueList (except for macros for UDTs, those are covered in Serialization refactor: macros for the new traits #802) - can be split over several PRs if needed,
• Adjust the codebase to use the new serialization traits instead of the old ones (Session::query, Session::execute, _iter versions, etc.).

[Lorak-mmk]

This was done, in many PRs:
#887
#881
#880
#878
#871
#870 (succeeded by #881)
#869
#862
#858
#855
#851
#819