Add support for keyboard-interactive auth via userAuthCb

[devin-ai-integration]

Add support for keyboard-interactive auth via userAuthCb

This PR adds support for keyboard-interactive authentication using the userAuthCb callback, while preserving backward compatibility with the existing wolfSSH_SetKeyboardAuthPrompts method.

Changes

1. Modified the SendUserAuthKeyboardRequest function to:

   • Set responseCount to 0 when calling userAuthCb for prompt setup
   • Check for WOLFSSH_USERAUTH_SUCCESS_ANOTHER return value to proceed with sending prompts
   • Fall back to the existing keyboardAuthCb method if userAuthCb is not set or doesn't return SUCCESS_ANOTHER

2. Added documentation to wolfssh/ssh.h explaining the new keyboard-interactive authentication flow

3. Created tests in tests/auth.c to verify both authentication methods:

   • Added a useUserAuthCb flag to control which authentication method to test
   • Created test functions to verify basic and multi-round authentication via userAuthCb
   • Modified the server setup to conditionally use either authentication method

How It Works

When a keyboard-interactive authentication request is received:

1. The userAuthCb is called with responseCount set to 0
2. If the callback returns WOLFSSH_USERAUTH_SUCCESS_ANOTHER, the code proceeds with sending prompts
3. If the callback returns any other value or is not set, it falls back to the existing keyboardAuthCb method

This implementation preserves backward compatibility while adding the requested functionality.

Testing

Added tests to verify both authentication methods work correctly.

Link to Devin run: https://app.devin.ai/sessions/55433dc32bf946d397bcc854e1cbf66f
Requested by: andrew@wolfssl.com

[devin-ai-integration]

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[wolfSSL-Bot]

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