WIP: remove `ToAnyParam` and use `Into<Param>` instead

[divarvel]

Continuation of #302

The goal is to:

• remove the possibility of passing a public key where a term is expected
• remove ToAnyParam in favor of Into<AnyParam> for simplicity
• (possibly) extend the passing of public keys to support multiple keys at once, and keywords.

The main difference is that ToAnyParam takes a reference, while Into consumes its input.

todo

• [x] try using Into<Term> instead of T: ToAnyParam
• [ ] try using Into<(PublicKey, Vec<PublicKey>)> instead of PublicKey