refactor(core/mercury): separate upy args parsing

[obrusvit]

This PR separates the Rust flows from micropython layer.

The idea is to do the uPy argument parsing in ui/model_mercury/layout.rs and then pass them as regular arguments to code in ui/model_mercury/flow/**.rs, i.e. they won't be passed as args: &[Obj], kwargs: &Map. The goal is to keep the rust flows independent from micropython sub-crate. This separation is done for two reasons:

• it simplifies the code in for flows creation which
• it paves the way for apps done completely in Rust

This PR has no impact on UI or features.

TODO:

• [x] some lifetime issues to FIX
• [x] there is a few places with the usage of Obj and IterBuf
  • last place is get_address.rs, postponing this for now