Steps to reproduce:
----------------------------------
1. Install `l10n_ch_hr_payroll_elm_transmission` module
2. Switch to Swiss company
3. Navigate to Payroll > Transmission > BVG-LLP Basis Declaration
4. Create two Reports with same Year and Month
5. Now try to create new Employee from the employee app

Observation:
----------------------------------
Tracaback Occurs:
```
 File '/home/odoo/src/enterprise/19.0/l10n_ch_hr_payroll/models/l10n_ch_employee_monthly_values.py', line 319, in _compute_bvg_lpp_annual_basis
    existing_declaration = max(existing_declaration, key=lambda r: r.month) if existing_declaration else False
                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File '/home/odoo/src/odoo/19.0/odoo/orm/models.py', line 5934, in ensure_one
    raise ValueError('Expected singleton: %s' % self)
ValueError: Expected singleton: l10n.ch.lpp.basis.report(1, 2)
```

Issue:
----------------------------------
In the following code:
https://github.com/odoo/enterprise/blob/44a26539093f9313d9cd5f823c11866e3c98ec97/l10n_ch_hr_payroll_elm_transmission/models/l10n_ch_employee_monthly_values.py#L319-L320

Python's max() function doesn't just call the key function once per item. When there are ties (equal key values), it may need to compare the original objects, and during this process, Odoo's recordset operations combine records, causing the lambda receives `r` as a combined recordset. To access `.month` on a multi-record recordset it gives singleton error.

Solution:
----------------------------------
Creates tuples of (month, recordset) pairs and uses max() to compare month integers directly, avoiding the singleton error.

opw-5391742

## Short functional explanation of the error
When creating a public Time off for a Working Schedule, the end date will automatically set to a moment earlier than the set start date if the start date hour is set to midnight sharp.

## Reproduction Steps
1. Go to Employees.
2. Click on Configuration tab > Working Schedules.
3. Select a Working Schedule.
4. A smart button Public Time Off should appear. Click on it.
5. Click New and select a Start Date with a random date but 00:00:00 as hours:minutes:seconds.

### Expected behavior
The End date should automatically set 23 hours 59 minutes and 59 seconds later.

### Unexpected behavior
A Validation error occurs and the end date is set 1 second before the start date.

## Origin of the issue
When setting automatically the end date of a leave, it is set to 23:59:59. With our timezone, if we select midnight, this time will be converted to 23:00:00, the day before:
https://github.com/odoo/odoo/blob/e85f1a182ee60a25905369c84ced05480c5a3360/addons/resource/models/resource_calendar_leaves.py#L69-L70 Thus, the resulting end date will be set to the day before, at 23:59:59.
Additionally, we have to take into account the timezone of the user to set a consistent end date, and not the generic utc one.

__
opw-5187977



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- Some lots were found to contain very large delivery sets (7k+ picking IDs) with multiple parents.
- Updating parent sets in a single operation caused a MemoryError for large datasets.

```sql

Traceback (most recent call last):
   File "/tmp/tmpe5fq5baf/migrations/base/tests/test_mock_crawl.py", line 333, in crawl_menu
    self.mock_action(action_vals)
   File "/tmp/tmpe5fq5baf/migrations/base/tests/test_mock_crawl.py", line 346, in mock_action
    return self.mock_act_window(action)
   File "/tmp/tmpe5fq5baf/migrations/base/tests/test_mock_crawl.py", line 506, in mock_act_window
    mock_method(model, view, fields_list, domain, group_by)
   File "/tmp/tmpe5fq5baf/migrations/base/tests/test_mock_crawl.py", line 539, in mock_view_form
    [data] = record.read(fields_list)
   File "/home/odoo/src/odoo/18.0/odoo/models.py", line 3858, in read
    return self._read_format(fnames=fields, load=load)
   File "/home/odoo/src/odoo/18.0/odoo/models.py", line 4089, in _read_format
    vals[name] = convert(record[name], record, use_display_name)
   File "/home/odoo/src/odoo/18.0/odoo/models.py", line 7078, in __getitem__
    return self._fields[key].__get__(self)
   File "/home/odoo/src/odoo/18.0/odoo/fields.py", line 1311, in __get__
    self.compute_value(recs)
   File "/home/odoo/src/odoo/18.0/odoo/fields.py", line 1493, in compute_value
    records._compute_field_value(self)
   File "/home/odoo/src/odoo/18.0/addons/mail/models/mail_thread.py", line 442, in _compute_field_value
    return super()._compute_field_value(field)
   File "/home/odoo/src/odoo/18.0/odoo/models.py", line 5297, in _compute_field_value
    fields.determine(field.compute, self)
   File "/home/odoo/src/odoo/18.0/odoo/fields.py", line 110, in determine
    return needle(*args)
   File "/home/odoo/src/odoo/18.0/addons/stock/models/stock_lot.py", line 149, in _compute_delivery_ids
    delivery_ids_by_lot = self._find_delivery_ids_by_lot_iterative()
   File "/home/odoo/src/odoo/18.0/addons/stock/models/stock_lot.py", line 385, in _find_delivery_ids_by_lot_iterative
    delivery_by_lot[parent_id].update(delivery_by_lot[lot_id])
 MemoryError

(Pdb)len(all_lot_ids)
22166
(Pdb)len(barren_lines)
9682
(Pdb)len(lots_to_propagate)
9682

Lot_id 11412: delivery_by_lot size = 7420, parents = 3

Lot_id 11753: delivery_by_lot size = 0, parents = 7

Lot_id 12845: delivery_by_lot size = 11, parents = 5

Lot_id 14646: delivery_by_lot size = 12, parents = 2

Lot_id 15801: delivery_by_lot size = 1700, parents = 3

Lot_id 19817: delivery_by_lot size = 0, parents = 4

Lot_id 22370: delivery_by_lot size = 0, parents = 1

Lot_id 25072: delivery_by_lot size = 6827, parents = 2

Lot_id 25134: delivery_by_lot size = 3, parents = 2

Lot_id 25135: delivery_by_lot size = 1, parents = 2
```
- Previous fix adds all child deliveries, even if some already exist, but this new patch adds only the missing ones

UPG - 3869661
OPW - 5900313

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