The Vision

For signing extrinsics, users can currently:

• Enable the "substrate-compat" feature to pull in Substrate crates and use these to sign transactions
• Hand off a signer payload to some external thing to sign it.

I'd like to provide signer logic built-in to Subxt, so that "substrate-compat" is not needed in most cases (reducing number of crates puleld in by ~200 last time I checked). Hopefully this will speed up build times and provide a nice self contained way to experiment with building and signing transactions.

The plan

• Support generating keypairs (ideally from phrases too) and basic signing logic in Subxt (possibly behind a feature flag if it ends up pulling in a bunch of deps, and possibly as a subxt-signing crate or similar).