[BIP Draft] Segregated Data: a prunable, script-isolated block region for data carriage

Segdata and Segwit are distinct in their technical implementations and implications for blockchain operations. Segdata, unlike Segwit, is characterized by its unspendability and the fact that it is not mandatory to download during synchronization processes. Users have the option to opt out of retaining Segdata without affecting the validity of a block. This flexibility can be particularly advantageous for users concerned with storage and bandwidth efficiency. However, it's important to note that witness data, which is integral to both Segdata and Segwit, continues to impose burdens on initial block download (IBD) and unpruned storage requirements. These aspects are crucial for understanding the operational intricacies and trade-offs involved in implementing these technologies within blockchain systems.