Rewrite JS<->Rust type conversion

[adespawn]

Currently, we use the Complex Type to convert the Rust representation of the CQL type to the type info used in the JS encoder and user metadata.

We should consider rewriting this conversion, probably by materializing the desired object directly on the Rust side - depending on what leads to better performance.

We should also add a proper documentation on what this object should look like, as this is currently missing in the driver documentation.