CLI-only entrypoints

[zie1ony]

Sometimes it is useful to have some data getter, that not need to be deployed as entrypoint on chain.

Possible solution via labeling methods, but this might be tricky with traits, like we had problems when designing migrate method.

#[odra::module]
struct A {}

#[odra::module]
impl A {
    #[odra::cli]
    pub fn a(&self) -> u8 { 8u8 }
}

Or we allow for other impl.

#[odra::cli]
impl A {
    pub fn a(&self) -> u8 { 8u8 }
}