fix(vi_VN): update address formats, administrative units, and postcodes

[hmtrii]

What does this change

Updates the vi_VN address provider to generate more realistic and current Vietnamese addresses.

The changes include:

• Updated provincial-level administrative units.
• Updated five-digit postcode ranges.
• New building-number, sub-street, street, commune, city, and province generators.
• More representative full-address formats.
• Expanded tests covering the new generators and postcode behavior.

What was wrong

The provider contained outdated administrative-unit data, generated six-digit postcodes, and supported only limited Vietnamese address formats.

How this fixes it

The provider now uses the current administrative structure and postcode ranges while composing addresses from realistic Vietnamese address components.

Fixes #2432

AI Assistance Disclosure (REQUIRED)

• No AI tools were used in preparing this PR.
• If AI tools were used, I have disclosed which ones, and fully reviewed and verified their output.

AI assistance was used to help review the changes and draft the issue and pull request descriptions.

Checklist

• I have read the documentation about CONTRIBUTING
• I have read the documentation about Coding style
• I have run make lint