[FIX] stock: avoid flush all env in quants update

Issue:
The `_update_available_quantity` will flush the all environment due to
the savepoint (at each call). When we working with the package,
it becomes bottleneck due to the `_compute_package_info`. Indeed,
it computes two compute store field (`location_id` and `company_id`) and
depends of multiple field of related quants `quants_ids.xxx`. It means
that each time we enter/exit in the savepoint to update quants, this
compute will be execute (because of flush + compute_store).

Solution:
Avoid flushing when enter in the savepoint of
`_update_available_quantity` (`flush=False`)

Performance gain:
To validate a Delivery with 1000 move lines with package (source and
dest):
- Without patch: +- 120 sec
- With patch: +- 17 sec

opw-2371161

closes odoo/odoo#62841

X-original-commit: b2d57323caf9f7fe47c4fe9ac26b0e955d9987b9
Signed-off-by: Arnold Moyaux <amoyaux@users.noreply.github.com>
Signed-off-by: William Henrotin <Whenrow@users.noreply.github.com>

addons/stock/models/stock_quant.py

@@ -414,7 +414,7 @@ class StockQuant(models.Model):
 
         for quant in quants:
             try:
-                with self._cr.savepoint():
+                with self._cr.savepoint(flush=False):  # Avoid flush compute store of package
                     self._cr.execute("SELECT 1 FROM stock_quant WHERE id = %s FOR UPDATE NOWAIT", [quant.id], log_exceptions=False)
                     quant.write({
                         'quantity': quant.quantity + quantity,