Fix sign_memo command for signing with public keys

[abitmore]

Fix sign_memo command for signing with public keys, and add CLI tests

• more tests about read_memo and sign_memo
• formatter of account_update_operation in account history
• result formatter for SHA256 hashes in HTLC operations

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

100.0% Coverage
0.0% Duplication

[sschiessl-bcp]

What can we do with this (from user's viewpoint) that we could not do before?

[abitmore]

@sschiessl-bcp the existing feature makes it possible that memo to be readable by a 3rd party but not the recipient, by using a key the 3rd party provided, although the use case is not obvious. Before the changes offered in this pull request, the user need to add the key to cli_wallet with a label, then run the command with that label. After the change, the user can run the command with the key directly.

[sschiessl-bcp]

Thx for clarification.

What would be an example use case? Auditing?

[abitmore]

TBH I don't know. The feature is already there for a long time.
One use case I think is when the recipient doesn't have a valid memo key, the sender can still send the funds with a memo, and the memo is perhaps useful for the sender, e.g. for tracking.