[FIX] stock: improve perf of `_compute_has_packages` of `stock.picking`

Use read_group instead of search count to batch the compute.

opw-2371161

closes odoo/odoo#63754

X-original-commit: b82d8a8456085ab700ef1ce1df4052fa6cefd7e0
Signed-off-by: Arnold Moyaux <amoyaux@users.noreply.github.com>
Signed-off-by: Rémy Voet <ryv-odoo@users.noreply.github.com>