refactor: flatten nesting in org-drill-entries

The main loop body reached 7 levels of indentation in the success
path: while > destructuring-bind > save-excursion > cond > t-clause
> let > cond > inner-cond.

Extracted two helpers:

- org-drill--pick-next-marker: chooses between resuming the
  current-item slot and popping a fresh marker, returning a (marker
  . next-resuming-p) cons so the caller updates resuming-p in
  lock-step.
- org-drill--route-rating-result: routes the rating result into
  the session's again/done queues and returns a symbol (quit/edit/
  skip/next) telling the caller whether to break the loop.

org-drill-entries shrinks from 54 lines to 19, and the deepest
nesting drops from 7 levels to 4.

0 files changed, 0 insertions, 0 deletions