SDKs - Provide an arbitrary byte sign/verify

[barnjamin]

At the moment the Sign/Verify bytes functions prepend the domain separator MX prior to signing/checking. This is fine in the case that it is desired but if a user is trying to do something like validate a signature on a transaction for auth purposes it makes the processes awkward and the user has to write their own ED25519 sign/verify functions.

The SDKs should provide some rawsign/rawverify that does not prepend the domain separator.

[barnjamin]

This request is often meant to allow a "sign in" in a web3 context. In lieu of arbitrary byte signing maybe something like this arc would be useful

[barnjamin]

In fact, maybe this should just validate a transaction rather than arbitrary bytes?

[joe-p]

I think a function for arbitrary signing/verifying would be nice. If someone wanted to verify a transaction they could just leverage that. Ideally, I think we should have functions similar to the JavaScript SDKsignBytes and verifyBytes functions that don't make any requirements/assumptions about the "MX" prefix.

In my ideal world:

• signBytes is deprecated
• verifyBytes is deprecated
• signMessage to append bytes with "MX" and sign
• signRawBytes to sign any arbitrary data
• verifyRawBytes to verify any arbitrary data

[barnjamin]

A couple basic examples
https://github.com/barnjamin/sdk-extras/blob/master/py/verify.py
https://github.com/barnjamin/sdk-extras/blob/master/js/verify.ts