Fix/create add card form signature

[OttiaDevsPT]

Related tickets & documents

#55
https://inoob.atlassian.net/browse/PP6-126

What's Changed

Breaking Change: Refactored createAddCardFormRequest to internalize signature calculation and authentication parameters. This aligns the method with the rest of the SDK patterns and simplifies usage for developers. The AddCardFormRequest model no longer requires checkoutAccount, checkoutMethod, checkoutNonce, checkoutTimestamp, checkoutAlgorithm, or signature to be populated manually.

Features

• Internalized signature calculation for createAddCardFormRequest (matches createPayment pattern).
• Implemented Form Post style authentication (Body Auth) for add-card requests.

Refactoring

• Removed manual authentication fields from AddCardFormRequest model.
• Automatically injects merchant credentials and generates HMAC signature within the SDK.

Testing

• Added unit tests to verify signature generation and payload structure for card form requests.