Sibling Eviction for v3 transactions

The discussion centers around the implementation of a new feature in v3 transactions, which is deemed both desirable and straightforward due to the v3 rules' ability to determine the optimal sibling transaction to retain. This enhancement appears not to affect the existing strategy for lightning commitment transactions, where the preference remains to utilize a single ephemeral anchor to minimize the size of the commitment transaction. However, there's an alternative suggestion to eliminate the ephemeral anchor altogether and instead leverage other outputs from the commitment transaction for Child Pays for Parent (CPFP) purposes. While this idea is intriguing, it requires careful analysis to ensure safety and correctness across all scenarios.