Prevent Recursive Derivatives in IP Registration

[kingster-will]

Description

This PR includes changes that enhance the registerDerivativeIp function in the LicenseRegistry contract. The function now checks whether the child IP already has a child IP before registering it as a derivative. This change is aimed at preventing recursive derivatives in our IP registration process.

Changes:

1. Modified the registerDerivativeIp function to include a check for existing child IPs. If the child IP already has a child IP, the function will revert and prevent the registration.

2. Updated the unit tests to reflect these changes.

Test Plan

Add unit tests to cover to new code changes

[jdubpark]

For clarification, is this disallowing a root IP with existing children from becoming a child itself?

[Ramarti]

LGTM + Approved by auditors

[kingster-will]

For clarification, is this disallowing a root IP with existing children from becoming a child itself?

Yes, in that case, the number of children of the root IP would not be 0, hence the root IP cannot be a child itself.