[IMP] pos_self_order: Avoid extra _get_attributes_by_ptal_id calls

[zaha-odoo]

Description of the issue/feature this PR addresses:
This commit is a performance fix to improve the speed of opening the pos kiosk or QR code.

_get_attributes method of pos_self_order's product.product extension will call self.env["pos.session"]._get_attributes_by_ptal_id() every time it is called. For N products, _get_attributes is called N times. This can lead to slow performance for high enough N, because _get_attributes_by_ptal_id method is slow, because it makes many read calls to product.attribute.value

This commit lifts the call to _get_attributes_by_ptal_id higher in the call stack, so that it is only called once as opposed to N times. It passes its result into _get_attributes via context, which will re-call _get_attributes_by_ptal_id if it wasn't in context for backwards compatibility reasons.

attributes must be deep copied within _get_attributes, because _add_price_info_to_attributes mutates the values within, which would invalidate future calls. The deep copy gives a fresh instance for each call, and only copies the applicable attributes so it shouldn't be large.

In this particular customer's DB they have 1376 product.product records and their pos config's pricelist (id 36) has 1572 rules in it.

Overall, based on the benchmarks below, this commit makes loading the pos about 4-5 times faster.

Benchmarks:

Before commit

Customer DB
product.product count == 1376
SQL query count ~= 5034
Time to load pos ~= 44 sec

Customer DB with more products
product.product count == 3792
SQL query count ~= 9359
Time to load pos ~= 96 sec

After commit

Customer DB
product.product count == 1376
SQL query count ~= 2360
Time to load pos ~= 8 sec

Customer DB with more products
product.product count == 3792
SQL query count ~= 3906
Time to load pos ~= 22 sec

Current behavior before PR:
Slow loading of pos kiosk/QR code

Desired behavior after PR is merged:
Faster loading of pos kiosk/QR code

opw-3758923

[robodoo]

.

[caburj]

needs rebase

[zaha-odoo]

@caburj Can rebase this to a later version, would 17.0 be a good candidate for this? It is also the version of this customer's DB. Apologies for my lack of knowledge here, but would the reason for the rebase be for stability?

[caburj]

robodoo r+