[18.0][IMP] hr_expense_sequence: propagate number to journal entries

[JordiBForgeFlow]

Problem

hr_expense_sequence numbers expense reports (EX0001), but that number stops
at hr.expense.sheet. The accounting documents the report generates are
referenced by free text instead:

• employee-paid → the vendor bill gets ref = sheet.name (the report summary);
• company-paid → each payment entry gets ref = expense.name.

So there is no way to tie a payable line back to the expense report it came
from, and reconciling the accounts payable by report number is impossible.

What this does

The report number is prefixed onto the reference of every journal entry the
report generates:

	Before	After
Vendor bill (employee-paid)	Client visit	EX0001 - Client visit
Payment entries (company-paid)	Flight	EX0001 - Flight

account.move.line.ref is a stored, trigram-indexed related field on
account.move.ref, so the number lands on every journal item — searchable,
groupable and sortable from the reconciliation widget, the Journal Items list
and the Aged Payable report.

A prefix rather than a replacement, for two reasons:

• company-paid reports generate one entry per expense line; replacing the
  reference would give every entry of a report the same value and you could no
  longer tell the flight from the hotel;
• sorting journal items by Reference now groups a report's items together while
  each line still says what it was.

Searching by number is unaffected — the search view matches ref with ilike
on a trigram index.

Implementation

Two hooks, both taken after super() so the value being prefixed is whatever
core (or another module) decided:

• hr.expense.sheet._prepare_bills_vals() — employee-paid vendor bill;
• hr.expense._prepare_payments_vals() — company-paid payment entries.

_prepare_move_vals() is not enough on its own: both callers set ref
explicitly after spreading its result, so it would be overwritten.

Two non-obvious points, both commented in the code:

• ref and payment_reference are set to the same value. Core builds t
  payable line's label from both and concatenates them when they differ
  (account_move_line.py:_compute_name), so prefixing only ref would have
  produced EX0001 - Client visit - EX0001 on the AP line.
• The payment memo is set too. account.payment._inverse_memo writes
  onto account.move.ref, and payments are created after the moves in
  _do_create_moves, so setting the move reference alone is silently undone

Reports without a number (/) are left completely untouched. No new depende
— hr_expense already depends on account. Version bumped to 18.0.1.1.0.

Tests

tests/test_hr_expense_sequence_account_move.py, 6 tests: employee-paid bill

payments, a manually forced number, no number, and an empty reference (no
dangling separator).

Run green both standalone and with hr_expense_invoice installed — that mod
bypasses move creation on approval for employee-paid reports, so the tests
assert after action_sheet_move_post().

Not covered

• Entries created before installing this module keep their original
  reference; assign_old_sequences numbers the existing reports but does not
  rewrite their posted entries.
• Reversals lose the reference: core's _do_reverse_moves forces
  ref: False. They auto-reconcile against the original, so this does not b
  anything, but the number is not on them.

Find attached a video that shows the behaviour:

hr_expense_sequence_move_ref.mp4

[JordiBForgeFlow]

The error testing OCB seems to be unrelated https://github.com/OCA/hr-expense/actions/runs/30613090613/job/91100087880?pr=377#step:2:173