Shared Secret Fixes

[lydiagarms]

Summary

Fixes #472. This PR fixes two issues relating to shared secret variables and adds a more user friendly error message:

• Fixes a bug, where for shared secret variables that are modified in a function where there is a require statement such as require(msg.sender == admin), the ownership of the variable is assigned to the admin. This means the new commitment will be created under the admins public key and not the sharedPublicKey, which is what we want by default.
• Introduces a fix in the event listener for shared secret variables. Say there are shared between Clients A and B, when client A nullifies one of these variables it will update its own commitment DB, but client B will not know that the commitment is nullified. In this PR, when the commitment DB is accessed we check the nullification is update with the onchain state.
• Adds an error message, when in orchestration a usable commitment cannot be found.

Checklist

• Tests added/updated
• CI passes
• No secrets/keys committed
• Docs updated (if needed)
• Backwards compatible (or noted breaking change)

How to test

1. Test with Swap.zol where startSwap can only be called by an admin,