Implement the drain / secondary drain

[vincent-herlemont]

drain() is a method that allows removing elements while returning them via an iterator.

It needs to be implemented for primary and secondary, with scan queries such as all, range, and start_with. Inspiration can be taken from the scan implementation in src/transaction/query/scan/mod.rs.

NOTE: There is already an implementation for primary, but it should be looked at to see if improvements can be made.

• src/transaction/query/drain.rs#L9-L20
• possible improvements ...

TODO

• Improve primary drain
  • Implement primary drain all
  • Implement primary drain range
  • Implement primary drain start_with
• Implement secondary drain.
  • Implement secondary drain all
  • Implement secondary drain range
  • Implement secondary drain start_with