**Core delete tasks**:
- [x] Implement free page functionality
- [x] Clear overflow pages if any before deleting their cells using free
page.
- [x] Implement delete for leaf page
- [ ] Balance after delete properly
**Auxiliary tasks to make delete work properly**:
- [x] Implement block coalescing in `free_cell_range` to reduce
fragmentation.
- [x] Track page fragmentation in `free_cell_range`.
- [x] Update page offsets in `drop_cell` and update cell pointer array
after dropping a cell.
- [x] Add TCL tasks
Closes#455
--------
I will add support for balancing after delete once `balance_nonroot` is
extended. In the current state of `balance_nonroot` balancing won't work
after delete and corrupts page.
But delete itself is functional now.
Closes#785
7169706809