Multiple VAT legs, fix JEs on accounts with "Exempt", add vat return support for expense claims

[dvdl16]

Description

• feat: Refactor to support Journal Entries with multiple rows/legs linked to the tax account
  • Fixes [BUG] URGENT: VAT not calculated correctly for Journal Entries #42
• fix: JEs on accounts with "Exempt" classification are missing in the VAT return
  • Fixes [BUG] JEs with VAT Classification set to "Exempt" are not included in the Value-Added Tax Return #43
• feat: Add vat return support for expense claims
  • Fixes [Feature] VAT get transactions not working with HR Expense claims #41

Type of change

• Bug fix (change which fixes an issue)
• New feature (change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Tests

• Unit Tests have been updated or added, as required
• UI Tests have been updated or added, as required

Checklist:

• My code follows Naming Guidelines (DocType, Field and Variable naming)
• No Form changes / My code follows the Form Design Guidelines
• My code follows the Coding Standards of this project
• My code follows the Code Security Guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas / No comments necessary
• I have made corresponding additions/changes to the documentation
• All business logic and validations are on the server-side / No business logic or validation changes
• No patches are necessary / Migration Patches have been added to the correct subdirectory of /patches and patches.txt have been updated

User Experience:

[codecov]

Codecov Report

❌ Patch coverage is 86.17886% with 17 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...e/value_added_tax_return/value_added_tax_return.py	86.88%	16 Missing ⚠️
csf_za/__init__.py	0.00%	1 Missing ⚠️

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