[19.0][ADD] hr_expense_tax_distribution

[dnplkndll]

Adds the new module hr_expense_tax_distribution on 19.0.

Origin: ported from an internal Akretion working branch authored by Guillaume Masson guillaume.masson@akretion.com. The module does not exist on any earlier OCA series (14.0–18.0), so this is a fresh [ADD] to OCA/hr-expense rather than a [MIG] from a prior series — the [ADD] prefix also routes /ocabot merge to the right (minor) bump.

What it does

When a single expense receipt carries multiple VAT rates (a French restaurant bill at 5.5% / 10% / 20% is the canonical case), Odoo's stock tax_ids field can only carry one rate against the full total. This module adds a tax_line_ids one2many on hr.expense where the user splits the receipt total across as many tax-rate lines as needed, each holding a base amount and the applicable taxes; the resulting accounting move is built from those lines instead of the single tax_ids / total pair, producing a correct VAT breakdown. A _constraint_total_matches constraint blocks submit unless the distribution lines sum back to the expense total.

When no distribution lines are present (has_tax_distribution = False), the form hides the section and the module is a no-op — the expense flows through stock 19.0 paths unchanged.

Non-mechanical adaptations worth flagging

• Sheetless tax distribution. The original Akretion design aggregated tax lines on hr.expense.sheet. Odoo 19 collapsed expense reports into expense lines, so this port overrides _prepare_receipts_vals() and _prepare_payments_vals() on hr.expense directly to inject the per-rate tax lines into the accounting entry without going through the (now-removed) sheet model.
• Test modernisation. Replaced legacy sheet workflows + action calls in the unit tests with direct line submission and direct posting (_post_without_wizard), and converted assertions to the 19.0 expense.state / approval_state machine.
• Lazy translation refactor. Standardised on self.env._() throughout instead of module-level _().

Test coverage

tests/test_hr_expense_tax_distribution.py — 22 test methods covering: compute paths on hr.expense.tax.line (single tax, multi-tax, zero base, no tax); the has_tax_distribution boolean; onchange rebuild semantics when tax_ids changes (adding, removing, preserving base amounts); the sum-matches constraint (matches, mismatches, zero-total, negative-base); and the accounting move generation (price_unit × quantity, account move amounts).

[dnplkndll]

Replaced by #351 — source branch moved from dnplkndll fork to ledoent organization fork. Same commits (HEAD 4f05f21), no content change.