fix(deriv_auth): Refactor isSvgAccount check using landing_company API

[aliakbar-deriv]

Clickup link:
https://app.clickup.com/t/20696747/GRWT-6679
https://app.clickup.com/t/20696747/GRWT-6683

This PR contains the following changes:

This PR updates the isSvgAccount method to improve accuracy in detecting whether an account is associated with SVG (St. Vincent & the Grenadines) by removing reliance on upgradeableLandingCompanies, which is no longer a reliable source for wallet accounts. And, setting the default account type in NewVirtualAccountRequestModel to 'dynamic' to support the wallet signup use case.

• ✨ New feature (non-breaking change which adds functionality)
• 🛠️ Bug fix (non-breaking change which fixes an issue)
• ❌ Breaking change (fix or feature that would cause existing functionality to change)
• 🧹 Code refactor
• ✅ Build configuration change
• 📝 Documentation
• 🗑️ Chore

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• ✍️ I have included clickup id and package/app_name in the PR title.
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• ⚒️ I have fixed any errors/warnings shown by the analyzer/linter.
• 📝 I have added documentation, comments and logging wherever required.
• 🧪 I have added necessary tests for these changes.
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@ahrar-deriv

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