WIP

Flush all segments in two stages:

1. inserts and updates
2. deletes

This is a naive implementation that allows us to test this idea. If it works out, we can polish it further.

We've seen a variety of issues where points did go missing. Almost all of them are related to us deleting them on disk too early. Segments have a strong dependency with each other in terms of flushing order to ensure data consistency.

The rough idea of this change is to always flush deletes as very last step. This will hopefully prevent all such issues. We rely on the WAL to repair all cases where we might have partially flushed.

All Submissions:

• Contributions should target the dev branch. Did you create your branch from dev?
• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

New Feature Submissions:

1. Does your submission pass tests?
2. Have you formatted your code locally using cargo +nightly fmt --all command prior to submission?
3. Have you checked your code using cargo clippy --all --all-features command?

Changes to Core Features:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your core changes, as applicable?
• Have you successfully ran tests with your changes locally?