Enhance payment processing and admin dashboard filtering

[rsmoke]

This pull request introduces several improvements and fixes related to payment handling, admin dashboard filtering, and test coverage for conference-closed scenarios. The main focus is on refining the logic for special invitees, enhancing payment amount validation to support decimal-formatted inputs, and adding comprehensive request specs for the conference closed page. Additionally, test support files are updated to better control when mocks are used.

Payment handling improvements:

• Updated validated_payment_amount in PaymentsController to accept whole-dollar amounts formatted as decimals (e.g., "50.0" or "50.50" are now parsed as 50), improving compatibility with external systems and database values.
• Adjusted payment specs to verify new behavior for decimal-formatted amounts, ensuring that values like "50.50" are truncated to whole dollars and accepted. [1] [2]

Admin dashboard and filtering:

• Refined the selection of special invitees on the admin dashboard to include only users with the account_type of "special", excluding "scholarship" and other types. Related test expectations were updated accordingly. [1] [2] [3]
• Added a filter for account_type in the admin payments index, allowing admins to filter payments by account type.

Test coverage and support improvements:

• Added a comprehensive request spec for the conference closed page, covering various user states and ensuring correct messaging and button visibility.
• Enhanced test support files to allow opt-out of mocks via metadata (real_application_settings), enabling tests to use real database rows when necessary. [1] [2]