Pull current stacks signer out into v1 implementation and create placeholder v0 mod

[jferrant]

Closes https://github.com/stacks-network/stacks-core/issues/4783

Didn't want to do too many changes at once in case I inadvertently broke things. I am sure there is some further break down that could be done but think this is a good start.

EDIT: Confirmed both failing tests are flakey or consistently failing in develop already.