cosmrs: refactor Msg* traits

[tony-iqlusion]

• Removes the former Msg newtype for Any; uses the Any type explicitly. The Msg newtype was providing little value and obscuring access to the type_url.
• Renames from_msg and to_msg methods to from_any and to_any.
• Renames the MsgType trait to Msg. This trait now has an associated Proto type bounded on MsgProto. This alows for default impls of from_any/to_any/into_any methods which replace the previous blanket impl of MsgType for MsgProto.

Altogether these changes simplify the API and eliminate some redundant
boilerplate impling the former MsgType trait.

[tony-iqlusion]

There are a lot of changes in this PR that are just churn because the new trait design eliminates a lot of previous repetitive boilerplate, so perhaps I can break it down a bit and make it easier to review.

The main changes of note are all in msg.rs, namely:

The struct Msg newtype has been removed; replaced with Any

It used to look like this:

/// Transaction messages
#[derive(Clone, Debug, PartialEq)]
pub struct Msg(pub(crate) Any);

But really its usage is synonymous with Any. At the very least the pub(crate) provides no value because it doesn't maintain an invariant.

This also means that tx::Body::messages is a Vec<Any> instead of Vec<Msg>. However that's not to strange as Any is already used for tx::Body::extension_options and tx::Body::non_critical_extension_options.

MsgType is now just Msg; has an associated Proto type

This is a trait for "domain types", which each have a corresponding Proto type, and is bounded on TryFrom and Into conversions to the proto type.

It provides two default methods from_any and to_any that take care of serializing the proto and wrapping it in an Any to simplify serialization, leveraging the TryFrom and Into bounds.

The many changes you see across other files are handwritten implementations of from_msg and to_msg being replaced by the default implementations of from_any and to_any across the many message types currently defined in the crate.

[andynog]

Overall looks good to me. I think it's mostly proto changes and the ErrorReport. The new Msg methods seem fine to me.