Update `SchemaDiff.checkImplements` to emit ADDITION events for new interfaces.

* Add a loop to iterate over new interfaces and check if they are present in old interfaces.
* Emit an ADDITION event if a new interface is not present in the old interfaces.
* Retain the existing behavior with respect to interface removals.

Add a new test case in `SchemaDiffTest.groovy` to verify that `checkImplements` emits ADDITION events for new interfaces.

* Add a test case to cover scenarios where new interfaces are added and old interfaces are removed.

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