[17.0][IMP] account_financial_report: Add support for company branches

[Darumait]

This improvement adds multi-branch support to the financial reports generated by the account_financial_report module.

Key features:

• When a parent company is selected, the report automatically includes all branches (child companies) under it.
• Users can still generate reports for a single branch (subsidiary) if needed by selecting that specific company.
• Branch context is now respected across filters and report computations.
• Ensures accurate and consolidated financial reporting in multi-company, multi-branch environments.

This update enhances usability for businesses structured with a main company and multiple operational branches.

No changes to existing functionality in single-company or flat company structures.