[#347] Implement support for secp256k1 and P256 in Morley.Nettest.Pure

Description

Problem: Previously Morley.Nettest.Pure supported only ed25519.

Solution: AliasData is updated to contain a SecretKey instead of a Ed25519.SecretKey.

Related issue(s)

Resolves #347 (closed).

✅ Checklist for your Merge Request

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