Cached functions with `@ormcache` should not return immutable values, yet `_get_parameter_from_code()` could return dicts/sets/lists/etc.

It could lead to very obscure bugs such as:

```python
def some_innocent_code():
    category_dict = self.env["hr.rule.parameter"]._get_parameter_from_code('l10n_be_work_entry_categories')
    incapacity_codes = category_dict['partial_incapacity']
    incapacity_codes |= category_dict['total_incapacity']
    # ... then use incapacity_codes

def print_rule_param():
    print(self.env["hr.rule.parameter"]._get_parameter_from_code('l10n_be_work_entry_categories')['partial_incapacity'])

print_rule_param()  # OrderedSet(['LEAVE281'])
some_innocent_code()
print_rule_param()  # OrderedSet(['LEAVE281', 'LEAVE264', 'LEAVE266', 'LEAVE217', 'LEAVE218', 'LEAVE219', 'MEDIC01'])
```

The solution was to either deepcopy the returned value each time, or to change all the rule parameters to their frozen equivalent. Since we don't have access to frozen objects in rule parameters's xml definitions, we opted for the deepcopy approach.

task-6329380

Forward-Port-Of: odoo/enterprise#124141
Forward-Port-Of: odoo/enterprise#123057

Steps to reproduce:
------------------------------------------------
1. Install Event module
2. Create a multi day event
3. Create one attendee for the event
4. Change the event dates
5. Go to attendee and Click on Send by Email

Observation:
------------------------------------------------
The event start date displayed in the email body is not updated after the event dates are modified.

Issue:
------------------------------------------------
In `saas-18.2`, `event_begin_date` and `event_end_date` were simple related fields that automatically updated when their source fields changed. https://github.com/odoo/odoo/blob/saas-18.2/addons/event/models/event_registration.py#L57-L58

However, in `saas-18.3`, slots were introduced and these fields were converted to computed fields
https://github.com/odoo/odoo/pull/205945/changes/e2bf8a89d6a50bd40f4673bef38176465f83ba0f

* `event_begin_date` is made stored for cohort view grouping
* However, the base compute method only depends on `event_id` and `event_slot_id`
https://github.com/odoo/odoo/blob/ac37b479321dbe9dbf864e833900e043b1cc70df/addons/event/models/event_registration.py#L177-L180
* When you change `event.date_begin` or `event.date_end`, the registration records don't recompute because the dependency is on the `event_id`, not on the related date fields (`event_id.date_begin`, `event_id.date_end`)
* Non-stored computed fields recalculate on-the-fly when accessed, so `event_end_date` appeared to work
* Stored computed fields only recalculate when their explicit dependencies change

Solution:
------------------------------------------------
* Corrected the dependencies of `_compute_event_begin_date` to recompute
value on changing the date of the event

opw-6284576

Forward-Port-Of: odoo/enterprise#120184

Problem: When importing XML files to generate vendor bills, the system uses UBL parser and assumes that the PriceAmount node needs to be divided by the BaseQuantity node to obtain the exact price unit. However, in Colombia, the DIAN treats the PriceAmount node as the exact price unit. This was not flagged in the system so the parser incorrectly divides the PriceAmount by BaseQuantity, resulting in negative discounts to be added to match the subtotal.

Solution: Extract the basis_qty logic into a helper method so
other localizations can override when needed.

Current behavior: When importing a Colombian XML with a product that has a BaseQuantity greater than 1, the PriceAmount gets incorrectly divided, resulting in negative discounts on the vendor bill.

Expected Behavior: When importing a Colombian XML with a product that has a BaseQuantity greater than 1, the PriceAmount gets parses as the exact unit price with no negative discounts applied.

task-6215466

Forward-Port-Of: odoo/enterprise#122313