Add animation unit tests

[ralphweng2023]

Description

Adds comprehensive automated unit tests for animation functions in SplashKit. The existing test_animation.cpp provides manual/interactive testing, but lacked automated unit tests that can be run as part of CI/CD pipelines.

This PR adds unit_test_animation.cpp which provides automated tests for:

Animation Script functions:

• load_animation_script, free_animation_script, free_all_animation_scripts
• has_animation_script, animation_script_named, animation_script_name
• animation_count, has_animation_named, animation_index

Animation functions:

• create_animation (multiple overloads with/without sound)
• free_animation, assign_animation (multiple overloads)
• animation_name, animation_current_cell, animation_ended
• animation_entered_frame, animation_frame_time, animation_current_vector
• update_animation, restart_animation

Edge case handling:

• Null/invalid pointer handling for all getter functions
• Invalid script file loading
• Animation lifecycle testing (create → update → end → restart)

The tests use the existing kermit.txt animation script resource and follow the same patterns as other unit tests in the project.

Type of change

• New tests

How Has This Been Tested?

Built the test project using CMake as per build instructions. All tests pass successfully.

Automated Testing:

cd projects/cmake
cmake --preset macOS
cmake --build build/

cd ../../bin
./skunit_tests "[animation],[animation_script]" --success
# Result: All tests passed (86 assertions in 9 test cases)

./skunit_tests --order rand
# Result: All tests passed (1349 assertions in 88 test cases)

Testing Checklist

• Code compiles without errors
• All 9 new animation test cases pass (86 assertions)
• All existing tests still pass (88 total test cases, 1349 assertions)
• Tests run independently in random order

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code in hard-to-understand areas
• My changes generate no new warnings
• New tests have been added to prove the functionality works