## Current behavior:
The unpaid leave count for some employees is calculated incorrectly. As
a result, the work entries are generated incorrectly, which leads to
incorrect payslip creation.
- For the first half-day unpaid leave, the system correctly counts 0.5 days.
- When the same employee applies for another half-day unpaid leave on a
different day, the system incorrectly counts it as 0.05 days instead of
0.5 days.
- For some employees, even when they apply for a half-day leave, the
system counts 0.00 days.

## Expected behavior:
When an employee applies for half-day unpaid time off, the system should
count it as 0.5 days

## Steps to reproduce:
1. Employee with attendance or working-schedule work entry source
2. Check in, approve half-day unpaid leave, check out
3. Generate payslip — leave missing
4. Apply a second half-day leave — duration may show 0.05 or 0.00

## Causes of the issue:
- `_cancel_work_entry_conflict()`: skipped leave work entry creation, so no
leave work entry was created until refuse/re-approve or manual
regeneration
- `_get_durations()`: wrong calculations, could yield 0.00 days or 0.05
days for half-day off requests

## Fix:
- `hr_work_entry_holidays`: Generate work entries for the leave period when
needed, always create leave work entries after ensuring generation
- `hr_holidays`: sets days to half day off (0.5) for single-day half-day
requests. Keep half-day rounding for multi-day duration-based requests

opw-6353480