Improve logging of the PreApprovalElement decoding

[Hopsaheysa]

#227

[Copilot]

Pull Request Overview

This PR improves error logging for JSON deserialization failures in operation UI data parsing and adds test coverage for malformed JSON structures.

• Enhanced error visibility by upgrading log levels from warning/debug to error for JSON deserialization failures
• Added test coverage for incorrect JSON structure handling (object instead of array for elements)

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
library/src/main/java/com/wultra/android/mtokensdk/api/operation/utils/JsonHelpers.kt	Upgraded log levels from w/d to e for type mismatches and deserialization failures, and improved null handling with early returns
library/src/androidTest/java/OperationUIDataTests.kt	Added test case for Screen3 with incorrect elements structure to verify graceful error handling and null fallback behavior