[FIX] stock: unlink move_lines in batch

Before this patch, cancelling a PO of 2000 lines would take a **very,
very** long time to process... so long that I terminated it before it
finished... yikes.

This was due to the call to `_do_unreserve` on every single move when
calling `_action_cancel`, this meant that n² calls to unlink where being
made (at least), which also meant n² calls to
`stock.move._recompute_state` were being made... that's a lot of
recomputes... = bad performance

The patch simply calls unlink once, which means `_recompute_state` is
called only once, saving a lot of time.

Cancel time for a PO containing 2000 lines:
        - Before patch: 1h30min+ (process terminated before finishing)
        - After patch: 7min

Other modules making use of stock and `_action_cancel` should also see
benefits from this patch

closes odoo/odoo#31787

Signed-off-by: Arnold Moyaux <amoyaux@users.noreply.github.com>

addons/stock/models/stock_move.py

@@ -1014,10 +1014,12 @@ class StockMove(models.Model):
     def _action_cancel(self):
         if any(move.state == 'done' for move in self):
             raise UserError(_('You cannot cancel a stock move that has been set to \'Done\'.'))
-        for move in self:
-            if move.state == 'cancel':
-                continue
-            move._do_unreserve()
+        moves_to_cancel = self.filtered(lambda m: m.state != 'cancel')
+        # self cannot contain moves that are either cancelled or done, therefore we can safely
+        # unlink all associated move_line_ids
+        moves_to_cancel._do_unreserve()
+
+        for move in moves_to_cancel:
             siblings_states = (move.move_dest_ids.mapped('move_orig_ids') - move).mapped('state')
             if move.propagate:
                 # only cancel the next move if all my siblings are also cancelled