Updated BIP for OP_CAT

The OP_CAT BIP proposal has recently received significant updates, which include the introduction of a rationale section and an expanded section dedicated to backwards compatibility. Additionally, there has been an update to the reference implementation. These modifications aim to enhance the proposal's clarity and effectiveness. The revised proposal is accessible through a pull request in the bitcoin/bips repository, available at https://github.com/bitcoin/bips/pull/1525. Furthermore, it is also documented as BINANA BIN-2024-0001, with its details hosted on the Bitcoin Inquisition's GitHub page at https://github.com/bitcoin-inquisition/binana/blob/master/2024/BIN-2024-0001.md. These updates play a crucial role in ensuring the proposal's alignment with current technological standards and compatibility requirements.