Uses a full-fledged serai-abi to do so.
Removes use of UncheckedExtrinsic as a pointlessly (for us) length-prefixed
block with a more complicated signing algorithm than advantageous.
In the future, we should considering consolidating the various primitives
crates. I'm not convinced we benefit from one primitives crate per pallet.
* Remove subxt
Removes ~20 crates from our Cargo.lock.
Removes downloading the metadata and enables removing the getMetadata RPC route
(relevant to #379).
Moves forward #337.
Done now due to distinctions in the subxt 0.32 API surface which make it
justifiable to not update.
* fmt, update due to deny triggering on a yanked crate
* Correct the handling of substrate_block_notifier now that it's ephemeral, not long-lived
* Correct URL in tests/coordinator from ws to http
