pos_cache is used to speed up opening POS in databases with large number of
products. In some cases it's still not enough and thousands of records cannot be
cached in a single request, because reading information may take more time than
maximum allowed.

As a workaround, this commit adds posibility to split request into few small
requests. To activate the feature set system parameter
``pos_cache.limit_products_per_request`` to appropriate value depending on your
server capacity.

---

opw-2439347

closes odoo/odoo#66539

Signed-off-by: pimodoo <pimodoo@users.noreply.github.com>

STEP:
* install pos_cache
* create some products (this step is not needed in demo database)
* open POS

BEFORE: error "TypeError: Object of type 'datetime' is not JSON serializable"

AFTER: no errors

WHY:
* Since Odoo 12 date fields are not strings: https://github.com/odoo/odoo/commit/960360afe478a8f7b9c456721b5591154952a37d
* Since Odoo 14 fields lists to read contains write_date:
https://github.com/odoo/odoo/commit/c6397ab3b3654da336a4269a81d5d91016baf520 --
see models.js

---

opw-2410334

closes odoo/odoo#62952

Signed-off-by: Ivan Yelizariev // IEL <yelizariev@users.noreply.github.com>

PEP-594 is deprecating a bunch of modules. As part of the cleanup, we
are also dealing with long deprecated modules, functions and aliases.

* `assert_` -> `assertTrue`
* `assertEquals` -> `assertEqual`
* `assertNotEquals` -> `assertNotEqual`
* `assertAlmostEquals` -> `assertAlmostEqual`
* `assertRaisesRegexp` -> `assertRaisesRegex`
* `assertRegexpMatches` -> `assertRegex`
* `base64.encodestring` -> `base64.encodebytes`
* `base64.decodestring` -> `base64.decodebytes`
* `inspect.getargspec` -> `inspect.signature`
* `inspect.formatargspec` -> `inspect.signature`
* `logging.warn` -> `logging.warning`

closes odoo/odoo#36863

Task: 2003936
Signed-off-by: Raphael Collet (rco) <rco@openerp.com>

Multi is the default api for methods, it is not necessary to explicitly
decorate methods with it, adds clutter and most people use it because
they see that the rest of the code uses it.

Done with `find . -type f -name '*.py' | xargs sed -i '/@api.multi/d'`

Adapt all code that was using `api.one` to recordset-style method and
remove any and all calls to `api.one` in preparation for its removal.

closes odoo/odoo#30412