RDKB-63834: Add unit tests for empty config file detection and fprintf failure paths in persistence.c

[Copilot]

Code review on the persistence corruption-handling changes requested test coverage for two new branches: empty-file skipping in fetchLocalConfigs() and fprintf failure handling in saveConfigToFile().

Test additions (UtilsTest.cpp)

• FETCHLOCALCONFIGS_EMPTY_FILE — uses an Invoke lambda on the fstat mock to set st_size = 0, asserts unlink is called via removeProfileFromDisk and the config list stays empty
• SAVECONFITOFILE_FPRINTF_FAILURE — mocks fprintf returning -1, asserts fclose and unlink are both called and the return is T2ERROR_FAILURE
• SAVECONFITOFILE_SUCCESS — covers the previously untested full success path
• Removes the stale /* SAVECONFITOFILE2 */ commented-out block

Mock fix (FileioMock.cpp)

With FORTIFY_SOURCE active (default on Ubuntu), the compiler replaces fprintf with an inline call to __fprintf_chk, bypassing the existing extern "C" int fprintf(...) override entirely. Added a matching __fprintf_chk interception that delegates to the same g_fileIOMock->fprintf() method:

extern "C" int __fprintf_chk(FILE* stream, int /*flag*/, const char* format, ...) {
    va_list args;
    va_start(args, format);
    int result = g_fileIOMock ? g_fileIOMock->fprintf(stream, format, args)
                              : vfprintf(stream, format, args);
    va_end(args);
    return result;
}

Misc

• Added .gitignore covering autotools and build artifacts.

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