crypto/ed25519: add comprehensive edge-case test vectors
crypto/ed25519: add comprehensive edge-case test vectors

This will allow us to make changes to the internals confidently, without
risking causing issues in consensus applications. It will also prevent
architecture-specific divergence, like #40475.

Fixes #40478

Change-Id: I8c2b31406ca88add6941f14d8df8cecb96379cde
Reviewed-on: https://go-review.googlesource.com/c/go/+/304349
Run-TryBot: Filippo Valsorda <4f40cda291c5f9634e1affd3db44947af61f705c@golang.org>
Reviewed-by: Roland Shoemaker <0d270388f2f92757a5de0f4bd891d3b392c44c4f@golang.org>
Reviewed-by: Katie Hockman <e321a8fd89c4908465ddaf8d5d0d62480efacb63@golang.org>
TryBot-Result: Go Bot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Trust: Filippo Valsorda <4f40cda291c5f9634e1affd3db44947af61f705c@golang.org>
Trust: Katie Hockman <e321a8fd89c4908465ddaf8d5d0d62480efacb63@golang.org>

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