A new chapter: Hive v4

Dear Hive Community,

I'd like to apologize for my lack of support and updates for Hive over the past year. Despite this, your commitment to the community has ensured that the package is still in a remarkably good state, and for that, I'm incredibly grateful.

As many of you know, I have spent a lot of time optimizing [Isar](https://github.com/isar/isar) to be as fast, reliable, and fun to use as possible. However, I recognize that a lot of you truly appreciate the simplicity of Hive. The thought of discontinuing Hive did cross my mind, but I now see a much more constructive way forward:

Over the next several weeks and months, I plan to invest my energy into the development of Hive v4. The primary focus will be to maintain the user-friendly interface and feature set that you've come to love. However, instead of continuing with the custom storage engine that has been causing several issues, we will transition Hive's data storage to Isar.

This significant change comes with several exciting advantages, including support for multiple isolates, significantly improving resource efficiency and reducing startup time, among others. Moreover, this will simplify the maintenance of Hive, ensuring its longevity through sustained support.

I cannot thank you enough for your continued support and use of Hive. Together, let's continue to make it a tool we all love and rely on. 💜

Simon

This issue is a roadmap announcement for Hive v4 rather than an actionable task, and it names no files, tests, or entry points. Start by reviewing the current storage-engine implementation and the existing Hive interface, then compare them with Isar's capabilities. Done would require a defined migration that preserves Hive's user-facing features while adding the stated storage and isolate improvements.

Written by the indexing model from the issue text.