IEX-2498 add endpoint coverage for new capital, mandates, and recurring URL flows

Add serialization/deserialization tests and mock payloads for Capital Dynamic Offers and Balance Platform Direct Debit Mandates APIs, including tax form summary URL assertions. Also update recurring live URL resolution to use the paltokenization live domain format with required live endpoint prefix, and validate both test/live recurring endpoint behavior in DetermineEndpoint tests.

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