feat(cli): add sign and verify to the account subcommand

[Meshiest]

Motivation

Signatures can be created/verified programmatically both from AleoHQ/sdk (web-ui via aleo.tools) and within leo but not from the official leo or snarkOS CLIs.

This PR creates two straightforward commands for working with Aleo signatures:

• leo account sign [--private-key-file <privateKeyFile>|--private-key <privateKey>] -m <message> -s [seed] [--raw]
  outputs an Aleo signature of the message, signed with the private key.
• leo account verify -s <signature> -m <message> -a <address> [--raw]
  outputs The signature is valid or The signature is invalid if the signature is verified or invalid respectfully.

By default, all messages are snarkVM values so signatures are compatible with the signature::verify leo operator. If the --raw flag is passed, the message will be parsed as bytes, which is compatible with the [AleoHQ/sdk].

If a private key is not specified from arguments, the CLI will attempt to load it from environment, then from a .env file.

Test Plan

No code outside of the new features were changed and test coverage is as follows:

• Signature creation (unseeded)
• Seeded signature creation
• Valid signature verification
• Invalid signature verification (message is incorrect)
• Invalid signature verification (address is incorrect)
• All of the above using plaintext messages (rather than aleo values)

Related PRs

• https://github.com/AleoHQ/snarkOS/pull/2909 - Near identical API on snarkOS (with the exception of this one having .env support)
• Update leo account command section with sign and verify subcommands welcome#334 - Documentation for these new commands

Screenshots

Signing raw messages

Generating a signature of an Aleo value (5field)

Verifying a signed Aleo value in leo playground.

program helloworld_unk5cko.aleo {
  transition main(public s: signature, a: address, m: field) -> bool {
      return s.verify(a, m);
  }
}

[d0cd]

LGTM!

[Meshiest]

documentation for this branch is available in this PR: ProvableHQ/welcome#334