[FW][FIX] account: compute tax ordering

[fw-bot]

Issue Description:
Currently, the order in which taxes are applied can vary based on the sequence they are entered in the invoice's Taxes field. This inconsistency arises when the tax list is not manually adjusted, leading to each tax having an identical sequence value. As a result, their hierarchy within the flatten_taxes_hierarchy function is determined by their input order rather than a defined sequence, causing unpredictable tax calculations.

odoo/addons/account/models/account_tax.py

Lines 611 to 632 in 56666f8

	def flatten_taxes_hierarchy(self, create_map=False):
	# Flattens the taxes contained in this recordset, returning all the
	# children at the bottom of the hierarchy, in a recordset, ordered by sequence.
	# Eg. considering letters as taxes and alphabetic order as sequence :
	# [G, B([A, D, F]), E, C] will be computed as [A, D, F, C, E, G]
	# If create_map is True, an additional value is returned, a dictionary
	# mapping each child tax to its parent group
	all_taxes = self.env['account.tax']
	groups_map = {}
	for tax in self.sorted(key=lambda r: r.sequence):
	if tax.amount_type == 'group':
	flattened_children = tax.children_tax_ids.flatten_taxes_hierarchy()
	all_taxes += flattened_children
	for flat_child in flattened_children:
	groups_map[flat_child] = tax
	else:
	all_taxes += tax
	if create_map:
	return all_taxes, groups_map
	return all_taxes

A tax sequence should be explicitly defined, and in cases where sequences are identical, organization by tax ID should be enforced.

Steps to Reproduce:

1. Navigate to the Account or Invoice app.
2. Go to Configuration > Taxes.
3. Create a new tax with the advanced option Affect Base of Subsequent Taxes and specify an amount.
4. Generate a new invoice and add a line item priced at 100.
5. Apply taxes in the Taxes column in the following order: 15% followed by the newly created tax, and note the total amount.
6. Repeat step 5, but reverse the order of the taxes.
7. Observe that the total amounts differ between the two sequences.

Proposed Solution:
To ensure that taxes are applied consistently regardless of input order, we will modify the flatten_taxes_hierarchy function to add sorting by id. If the sequences are identical, the sorting will depend only on the id, otherwise it will be based on the sequence. This setting ensures a predictable and logical process for applying taxes.

opw-3691765

Forward-Port-Of: #155414
Forward-Port-Of: #154167

[robodoo]

Pull request status dashboard.

[fw-bot]

This PR targets saas-16.2 and is part of the forward-port chain. Further PRs will be created up to master.

More info at https://github.com/odoo/odoo/wiki/Mergebot#forward-port

[fw-bot]

@ilru-odoo @smetl ci/runbot failed on this forward-port PR

[fw-bot]

@ilru-odoo @smetl this PR was modified / updated and has become a normal PR. It should be merged the normal way (via @robodoo)

[smetl]

@robodoo r+