Issue Credential v2 and Present Proof v2 format handling is difficult to follow

[dbluhm]

As an ACA-Py maintainer, following the logic of the format handlers, especially the selection of a format handler for a given input, is extremely difficult (for me at least) to follow. Lines like:

        cred_ex_record = await cred_manager.create_proposal(
            connection_id=connection_id,
            auto_remove=auto_remove,
            comment=comment,
            cred_preview=cred_preview,
            trace=trace_msg,
            fmt2filter={
                V20CredFormat.Format.get(fmt_api): filt_by_fmt
                for (fmt_api, filt_by_fmt) in filt_spec.items()
            },  # <--- this list comprehension
        )

Are just too dense for me to parse with reasonable effort. Normally, I'd just peel this apart and get over it but this is a consistent enough issue that I think it is worth addressing, if only for the sake of maintainability in the future.

No shade on the original authors -- I think this code is probably more intuitive in a TypeScript context -- but in the context of Python and ACA-Py, this methodology stands out.