[FIX] l10n_fr_fec: alleviate memory error when exporting too many move lines

We now split the export of the FEC files per batch of move lines. This was necessary, as the fetchall() ran on the cursor to get the results could return a huge amount of data on big databases, saturating the RAM.

This fix is not exhaustive, and memory consumption could be lowered by removing the need to convert the whole file to base 64 and write it in attachment. Those changes are not doable in stable ; further improvements will come to master.

OPW 3442579

closes odoo/odoo#130673

X-original-commit: d79f072a
Signed-off-by: de Wouters de Bouchout Jean-Benoît (jbw) <jbw@odoo.com>
Signed-off-by: Olivier Colson (oco) <oco@odoo.com>