ff 0.13 (#269)

* Partial move to ff 0.13

It turns out the newly released k256 0.12 isn't on ff 0.13, preventing further
work at this time.

* Update all crates to work on ff 0.13

The provided curves still need to be expanded to fit the new API.

* Finish adding dalek-ff-group ff 0.13 constants

* Correct FieldElement::product definition

Also stops exporting macros.

* Test most new parts of ff 0.13

* Additionally test ff-group-tests with BLS12-381 and the pasta curves

We only tested curves from RustCrypto. Now we test a curve offered by zk-crypto,
the group behind ff/group, and the pasta curves, which is by Zcash (though
Zcash developers are also behind zk-crypto).

* Finish Ed448

Fully specifies all constants, passes all tests in ff-group-tests, and finishes moving to ff-0.13.

* Add RustCrypto/elliptic-curves to allowed git repos

Needed due to k256/p256 incorrectly defining product.

* Finish writing ff 0.13 tests

* Add additional comments to dalek

* Further comments

* Update ethereum-serai to ff 0.13

crypto/ed448/README.md

@@ -3,8 +3,7 @@
 Inefficient, barebones implementation of Ed448 bound to the ff/group API,
 rejecting torsion to achieve a PrimeGroup definition. This likely should not be
 used and was only done so another library under Serai could confirm its
-completion. It is minimally tested, yet should be correct for what it has. The
-functions it doesn't have are marked `unimplemented!()`. This has not undergone
-auditing.
+completion. It is minimally tested, yet should be correct for what it has. This
+has not undergone auditing.
 
 constant time and no_std.