AuthSig improvements

[James-Mart]

This PR is mostly refactoring existing functionality:

1. Refactors the SPKI library that was previously coupled to AuthSig/RAuthSig, it is now its own library in the same namespace that can be independently linked
2. Minor improvement to the tester, starting to remove its dependency on the psibase::PublicKey type (secp256k1 keys), which is being deprecated.
3. Wraps AuthSig and AuthK1 in their own namespaces, to better isolate functionality that is specific to each auth library.

And there are a few additions also related to auth:

1. Adds some functionality to the AuthSig plugin (The ability to set the key of the caller, and the ability to create and return a new keypair in pem format)
2. Adds a new library (also in AuthSig namespace) for parsing PEM to PrivateKeyInfo. Basically the private key equivalent to the SPKI library, although there's no packing/unpacking logic because it's intended to be used for signing in tests, not as objects that can packed and sent to the node.

[swatanabe]

The libraries also need to be installed and there should be a way to refer to them from psidk.

[James-Mart]

Okay, I believe this is addressed