kademlia: shrink public API of `libp2p-kad`

[thomaseizinger]

Description

Currently, libp2p-kad has several public modules like handler that don't need to be public. This makes it much more likely that a change is breaking in practice despite likely being irrelevant to users. See #3504 for an example.

Implementation suggestion

We want to ship this as a non-breaking change, thus we should adopt a similar approach as done in #3238 where we first deprecate these modules with a note that they will be made private.

Are you planning to do it yourself in a pull request?

No.

[umgefahren]

Should I get the grant filecoin-project/devgrants#1421, I would include that.

[tcoratger]

@thomaseizinger Does #3738 solve this issue or is this issue more global and it therefore corresponds to the complete removal of the public modules for the moment notified as deprecated in #3738?

[thomaseizinger]

It is resolved by #3738, well spotted!